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Research ArticleElectrical Transport and Lowered Percolation Threshold inYBa2Cu3O7minus120575-Nano-YBa2ZrO55 Composites
Pullanhiyodan Puthiyaveedu Rejith Sukumariamma Vidyaand Jijimon Kumpukattu Thomas
Electronic Materials Research Laboratory Department of Physics Mar Ivanios College Thiruvananthapuram Kerala 695015 India
Correspondence should be addressed to Jijimon Kumpukattu Thomas jkthomasemrlyahoocom
Received 10 May 2014 Accepted 6 August 2014 Published 25 August 2014
Academic Editor Dong Qian
Copyright copy 2014 Pullanhiyodan Puthiyaveedu Rejith et alThis is an open access article distributed under the Creative CommonsAttribution License which permits unrestricted use distribution and reproduction in any medium provided the original work isproperly cited
We investigated the chemical reactivity and percolation characteristics of insulating nanocrystalline YBa2ZrO55
prepared bymodified combustion route and the YBa
2Cu3O7minus120575
superconductor composite system Structural analysis was done by using X-ray diffraction technique surface morphology of the samples was studied using scanning electron microscopy and electricaltransport measurements like critical transition temperatures (T
119888) and self-field transport critical current (J
119888) were done by using
standard four-probe technique It is found that in YBa2Cu3O7minus120575
-nano-YBa2ZrO55
composite system the superconductor andinsulator materials coexist as separate phases without any noticeable chemical reaction even after sintering at high temperaturesFurthermore percolation threshold and critical exponent are found to be 119881
119862= 03 119905 = 168 and 119906 = 27 And the analysis of the
current flow in the polycrystalline samples reveals weak link behavior in the majority of grain connections
1 Introduction
High temperature superconductors with transition tem-peratures above 77K in ceramic materials have receivedtremendous responsiveness because of their scientific andpractical potential The study of superconducting smallaggregates clusters or particles is very important from boththe fundamental and the technological standpoint [1ndash3] Itwill be significant to study the percolation and supercon-ductivity of composites involving superconductor insertedin an insulator medium Granular nature along with shortcoherence length [4] and large penetration depth [5] of hightemperature superconductors allows us to investigate thepercolation behavior fractal properties quantum size effectsthermal fluctuations and size effects on superconductivityThepercolation concept was first employed to describe super-conductors by Davidson and Tinkham [6] who analysedresistivity data of composite Nb
3SnCu wires For the growth
of high quality films the choice of substrate is vital A high119879
119888superconductor-insulator system is very difficult to obtain
without compromising the superconducting properties The
chemical nonreactivity of the substrate materials with super-conductors indicates their potential as substrates for filmdeposition The chemical compatibility of materials with thesuperconductor at the processing temperature is crucial Alsosuperconductor-insulator percolation studies are a mediumto understand the fundamental mechanism behind hightemperature superconductivity
A percolation model can be regarded as a collection ofpoints or occupied sites distributed in a space certain pairsof them are randomly linked [7] Its applications range fromtransport in amorphous and porous media and compositesto the properties of branched polymers gels complex ionicconductors and superconductors [8]There is a path betweentwo points 119860 and 119861 if a sequence beginning with 119860 andendingwith119861 can be found such that successive points in thissequence are linked This path may allow the flow of chargebetween two points if we regard the occupied sites as piecesof conductor The sites may be clustered such that pairs ofpoints belonging to the same cluster are connected but thereis no path between points belonging to different clustersCluster size (number of points in the cluster) increases
Hindawi Publishing CorporationInternational Journal of SuperconductivityVolume 2014 Article ID 768714 7 pageshttpdxdoiorg1011552014768714
2 International Journal of Superconductivity
with the number of linkages Some cluster may become ofinfinite size at some critical density of occupied sites Abovethis critical density known as percolation threshold (119881
119904)
the infinite cluster spans entire system and the system isin percolating state For instance in an ideal mixture ofconducting and insulator particles the conductivity is zerooutside the percolating region whereas it takes a finite valueinside this region
It was reported that perovskites could be beneficialfor incorporation into YBCO due to their similar crystalstructures relative to the host YBCO phase [9] There-after perovskite based additions have gained renewed inter-est as a class of materials that can be incorporated intoREBCO superconductor for dramatic improvements in thepinning properties [10ndash13] And a number of perovskiteslike Sr
2HoHfO
55[14] GdBa
2NbO6[15] Ba
2ErZrO
55[16]
YBa2ZrO55
[17] and so forth were being considered as sub-stratematerials for YBCOfilmdepositionHowever substrateselection presents particular challenges for the productionof high-quality high-temperature superconducting (HTS)films suitable for applications [18] In order to confirm theirchemical compatibility with YBCO it is important to studythe electrical transport and percolation behavior in thesesuperconductor-insulator composites Transport propertiesand percolation behavior of high 119879
119888superconductor-metal
composites have been reported extensively [19ndash24] Thegeneral form of the double perovskites is A
2BB1015840O6 where for
the present work A = Ba B = Y and B1015840 = Zr Paulose et alstudied percolation properties of Ba
2YZrO
6prepared by con-
ventional solid state route and YBa2Cu3O7minus120575
superconductorcomposite using temperature-resistivity measurement andreported that both superconducting and normal state perco-lation threshold values of the composite are around 35 volof YBa
2Cu3O7in the system [25] In the present work the
percolation behavior and nonreactivity of nanoparticles ofYBa2ZrO55
(YBZO) ceramic prepared through an autoignit-ing combustion technique mixed with bulk YBa
2Cu3O7minus120575
(YBCO) superconductors are studied The variations in themicrostructure sintering behavior sample density electricaltransport such as 119879
119888 and current carrying capacity are also
studied
2 Materials and Methods
Conventional technique of solid state route was used forthe preparation of YBCO superconductor by which highpurity Y
2O3 BaCO
3 and CuO were thoroughly mixed in the
stoichiometric ratio of Y Ba Cu = 1 2 3 The mixture wasthen calcined at 930∘C for 72 hours with two intermediatewet grindings High quality nanoparticles of YBa
2ZrO55
(YBZO) were synthesized through modified autoignitingcombustion technique as reported by Jose et al [26] Ina typical synthesis aqueous solution containing ions of YBa and Zr was prepared by dissolving high purity Y
2O3
in dilute HNO3 Ba (NO
3)2 and ZrOCl
2(99) in double
distilled water in a glass beaker Citric acid (99) was thenadded to the solution containing Zr ions which serves asthe complexing agent Oxidantfuel ratio of the system wasadjusted by adding nitric acid and ammonium hydroxide
200nm
Figure 1 TEMmicrograph of YBa2ZrO55
nanoparticles
and the ratio was kept at unity The solution containing theprecursormixture at a pH of sim70 was heated using a hot plateatsim250∘C in a ventilated fumehoodThe combustion productwas subsequently characterized as single phase nanocrystalsof YBa
2ZrO55 The YBCO and nano-YBZO were thoroughly
mixed in different ratios and made into rectangular pelletsof dimension 12 times 4 times 1mm These pellets were sinteredat temperature ranges from 975∘C to 1500∘C for 12 hourswith a heating rate of 3∘Cminute depending on the volumepercentage of YBHO in the composite material The sampleswere then cooled to 550∘C and kept 24 hours for oxygenationand then cooled to room temperature
The structural characterization of YBCO-nanocrystallineYBZO composites was done by powder X-ray diffraction(XRD) technique using a Bruker D-8 X-ray diffractometerwithNickel filtered Cu119870
120572radiationThe surfacemorphology
of the sintered samples was studied using scanning electronmicroscopy (SEM) (JEOL JSM 6390 LV) The qualitativeand quantitative elemental composition of the materials inthe compounds was studied using energy dispersive X-rayspectroscopy (EDS) JEOLmodel JED-2300The critical tran-sition temperatures (119879
119888) of the samples were measured using
standard four-probe technique For the samples with highervol of insulator a two-probe method was used to measuretheir resistivity For this experiment the entire data collectionwas run using a Lab VIEW 71 program on a PC This wasconnected to Keithley source meter 2440 and nanovoltmeter2182A along with lakeshore temperature controller equippedwith PT-111 platinum sensor using a GPIB connection Theelectrical contacts on the surface of the pellets were doneby adhesive silver paste after making a narrow scratch onthe sample surface The self-field transport critical current(119869119888) measurements were done at liquid nitrogen temperature
using the standard 1 120583Vcm criterion
3 Results and Discussion
The powder morphology of the as-prepared YBa2ZrO55
nanopowder was done by using transmission electronmicroscopy (TEM) and is shown in Figure 1 The resultsuggested that the self-aligned nanoparticles of YBZO are ofcuboidal shape with sharp grain boundaries andwith size less
International Journal of Superconductivity 3
20 30 40 50 60 70
2120579 (deg)
(f)
(e)
(d)
(c)
(b)
(a)
Inte
nsity
(au
)
203
210
014
114
115
400 223
413
406 420
lowast220
lowast400
lowast420
lowast422
lowast440
(f)
(e)
(d)
(c)
(b)
(a)
203
210
014
114
115
400 223
413
406 420
lowastlowast220
lowast400
lowast420
lowast422
lowast440
Figure 2 XRD pattern of different vol of nano-YBZOmixed YBCO superconductor ((a) = 0 (b) = 10 (c) = 30 (d) = 50 (e) = 70and (f) = 100)
than 20 nm The selected area electron diffraction (SAED)pattern shown inset to Figure 1 reveals that the YBa
2ZrO55
nanoparticles were crystallized with bright polycrystallinediffraction rings SAED patterns were composed of a numberof bright spots arranged in concentric rings The electronswere reflected and diffracted from crystallographic planesof the unit cells of the sample to produce bright spots Therings were diffuse and hollow showing that the products werecomposed of nanocrystals with different orientations Thisis indicative of the polycrystalline nature of the crystallitesbut the spotty nature of the SAED pattern could be dueto the fact that finer crystallites with related orientationswere agglomerated together resulting in a limited set oforientations
The X-ray diffraction (XRD) patterns of composites for0ndash100 vol of nano-YBZO in the YBCO system are shownin Figure 2 XRD patterns of composites show that all thepeaks could be indexed for orthorhombic YBa
2Cu3O7minus120575
andcubic YBa
2ZrO55
and there is no extra peak detectable Thisimplies that YBa
2ZrO55
and YBa2Cu3O7minus120575
remain as twodifferent separate phases in the composite even after severeheat treatment up to 1020∘C For YBCO-YBZO compositeswith 80 vol YBZO the sintering temperature was above theperitectic temperature of YBCO (sim1030∘C) and therefore theformation of a 211 phase with YBCO is expected but in thepresent study the XRD patterns did not show the presence ofa 211 phase in the system Thus the composites synthesizedare suitable for the percolation studies
The surface morphology of the composite samples wasillustrated by scanning electron microscopy (SEM) Figure 3shows the SEM images of different vol of nano-YBZOadded YBCO composites These indicate that the surface ofthe samples presents a crystalline character which is typical ofa polycrystalline ceramic material The YBa
2Cu3O7minus120575
grainsform groups which have appearance of clusters and thereis no detectable interface interaction between the YBZOand YBCO grains However there are different grain sizes
and a random orientation of grain boundaries whereby thepresence of different intergrain conductivities is expected
The effect of YBa2ZrO55
on the superconducting tran-sition temperature 119879
119888of YBa
2Cu3O7minus120575
was studied by fourprobe measurements for temperatures ranging from 77 to300K Variation of normalized resistivity with temperatureof the YBCO superconductor mixed with different volof insulating nano-YBZO samples is shown in Figure 4It is observed that the composite sample with less than50 vol of YBCO showed a metallic behavior and gave zeroresistivity superconducting transition temperature above liq-uid nitrogen temperature However the YBCO-nano-YBZOcomposite with 80 vol of YBZO showed a conductingbehavior there is no superconducting transition up to 77KThe resistivity of composites is dominated by YBZO forvolume less than 50 of YBCO with a significant drop of120588 occurring near these values of volume The absence of asuperconducting network through the composite sample ora low vol of YBCO may be the reason for this behaviorThese results show that when YBCO is sim30 vol or abovethere are interconnected networks of superconducting grainsfor the super current to pass through the composite materialbut for lower vol of YBCO the continuous networkof superconducting grains breaks away and the resistancebecomes nearly equal to that of pure insulator Hence thevalue of percolation threshold for the YBCO-nano-YBZOcomposite sample lies between 30 and 40 vol of YBCO inthe composite
The resistivity (120588) and temperature coefficient of resis-tivity 120572 = (1120588)(119889120588119889119879) at room temperature are shownin Figure 5 as a function of vol of YBCO (119881
119878) in the
composite In the normal state YBCO behaves as a metallicconductor and shows resistivity sim10 120583Ωm However theresistivity of composites is dominated by YBa
2ZrO55
forlower vol of YBCO with a significant drop of 120588 occurringnear 30ndash50 vol The behavior of 120588 correlates with that of 120572which increases sharply towards that of YBCO starting from
4 International Journal of Superconductivity
(a) (b)
(c) (d)
(e) (f)
Figure 3 SEM images of different vol of nano-YBZO mixed YBCO superconductor ((a) = 0 (b) = 10 (c) = 30 (d) = 50 (e) = 70and (f) = 100)
119881
119878sim 30 vol So if we assumed that the electrical transport
behavior in YBCO-nano-YBZO composites is percolativethe percolation threshold 119881
119862is between 03 and 04 Thus
the superconducting percolation threshold and normal statepercolation threshold values of YBCO-nano-YBZO compos-ites lie in the same range The electrical properties of thesuperconductor-insulator system can be described in [27 28]
120588 = 120588
119900(119881
119878minus 119881
119862)
minus119905 for 119881119878gt 119881
119862
120588
1015840= 120588
1015840
119900(119881
119862minus 119881
119904)
119906 for 119881119862gt 119881
119878
(1)
where 120588119900and 1205881015840
119900are constants 119881
119862is the critical volume
fraction of superconductor at which 120588 changes dramaticallyand is called the percolation threshold 119881
119878is the vol of
superconducting material in the composite and 119905 and 119906 are
the critical exponent describing the transport properties ofthe composite system The values 120588
119900 1205881015840119900 119905 and 119906 are found
from the log-log plot of 120588 versus (119881119878minus 119881
119862) and 1205881015840 versus
(119881
119862minus 119881
119904) with 119881
119862= 03 The value of 119881
119862is adjusted so that
the log-log plots of 120588 and 1205881015840 give a straight lineLog-log plot of 120588 versus (119881
119878minus119881
119862) for119881
119878gt 119881
119862 is shown in
Figure 6 which gave the exponents 119905 = 168 and 120588119900= 508 120583Ω
m And Figure 7 shows the log-log plot of 1205881015840 in functionof (119881119862minus 119881
119904) for 119881
119862gt 119881
119878system which gave the values
119906 = 27 and 1205881015840119900= 5831 times 104 120583Ω m Least square fits were
performed to determine the slope of the plots which gavethe values of exponents 119905 and 119906 However for an idealizedmetal-insulator system 119905 = 17 and 119906 = 07 [29] A greatnumber of experiments on conducting-insulator systemsshow percolation thresholds in agreement with percolation
International Journal of Superconductivity 5N
orm
alise
d re
sistiv
ity (120588
120588r)
10
05
00
50 100 150 200 250 300
Temperature (K)
(a)
50 100 150 200 250 300
Temperature (K)
10
05
00
(b)
10
05
00
(c)
50 100 150 200 250 300
Temperature (K)
10
05
00
(d)
50 100 150 200 250 300
Temperature (K)
10
09
08
07
(e)
50 100 150 200 250 300
Temperature (K)
Figure 4 Temperature-normalised resistivity graph for differentvol of nano-YBZO mixed YBCO superconductor ((a) = 0 (b)= 20 (c) = 50 (d) = 70 and (e) = 80)
theory [19ndash21] However there are few others which reportedvariation from the universal values [27 30]
The values of critical current densities (119869119888) measured for
different samples at zero applied magnetic field are shownin Table 1 The self-field 119869
119888is found to be decreasing on
the addition of nanocrystalline YBZO in YBCO A judiciousexplanation is the existence of larger defect density since 119869
119888
is more sensitive to the defect density The analysis of thecurrent flow in the composite samples reveals the weak linkbehavior in the majority of grain connections But this doesnot necessarily mean that weak (Josephson) grain couplingis absent in these samples However the number of strongergrain connectionsmust be significantly above the percolationthreshold [28] which is defined as the minimum fraction fora continuous current path
YBa2Cu3O7minus120575
superconductor will start to melt anddecompose when it is sintered at higher temperature
40
35
30
25
20
15
10
0500 02 04 06 08 10
50
45
40
35
30
25
20
15
Vol of YBCO
Tem
pera
ture
coeffi
cien
t of r
esist
ivity
(120572)
log 120588
(120583Ω
m)
Figure 5 Variation of (a) normal state resistivity 120588 and (b)temperature coefficient of resistivity 120572 = (119897120588)(119889120588119889119879) at roomtemperature for different vol of YBCO
20
18
16
14
12
10
minus07 minus06 minus05 minus04 minus03 minus02 minus01
t = 168 1205880 = 508 120583Ωmlo
g 120588(120583Ω
m)
Vc = 03
log(VS minus VC)
Figure 6 Log-log plot of 120588 versus (119881119878minus 119881
119862)
40
38
36
34
32
30minus10 minus09 minus08 minus07
u = 27 1205889984000 = 5831 times 104 120583Ωm
log 120588
998400(120583Ω
m)
Vc = 03
log(VC minus VS)
Figure 7 Log-log plot of 120588 versus (119881119862minus 119881
119878)
6 International Journal of Superconductivity
Table 1 Sintering temperature density and electric transport data of different YBCO-nano-YBZO composites
Vol of YBCO Vol of YBZO Sintering temp (∘C) Density (gm cmminus3) 119879
119888(K) Self-field 119869
119888(times104 Acm2)
100 0 975 535 92 14790 10 983 557 92 08880 20 990 566 905 02670 30 1000 575 89 00950 50 1015 584 82 mdash30 70 1120 588 mdash mdash20 80 1230 603 mdash mdash10 90 1370 615 mdash mdash0 100 1500 627 mdash mdash
The values of 119881119862 119905 and 119906 obtained for different systems
of composites vary due to many factors The critical expo-nents 119905 and 119906 are a measure of the order of interactionbetween normal metal and insulator The value for idealpercolation threshold is around 17 vol of metal in thesystem for a perfect metal-insulator composite without anyinteraction or reaction between the two The normal stateand superconducting percolation threshold values of YBCO-nano-YBZO (03 vol of YBCO) composites are in closerranges as expected for an idealized percolation system and arelower than those observed in conventionally preparedYBZO-YBCO (035 vol of YBCO) composite [25] This may bedue to the better chemical nonreactivity between YBCO andnano-YBZO Furthermore there is a negligible conductivitybelow percolation threshold while it is expected to be zeroin ideal percolative systemsThe nonreactivity of YBCOwithnano-YBZO even at high processing temperature also pointsto the fact that nano-YBZO is a suitable substrate for YBCOsuperconductor and thus to develop devices based on hightemperature superconductor films and junctions
4 Conclusion
In this paper we have studied the chemical reactivityand percolation behavior using electric transport mea-surements in polycrystalline YBa
2Cu3O7minus120575
superconductor-nano-YBa
2ZrO55
composite From structural analysis it isobserved that the mixture of materials YBa
2ZrO55
insulatorwith YBa
2Cu3O7minus120575
superconductor is a system where theparticles of superconductor and insulator materials are foundto coexist in a composite with two well-defined separatephases Resistivity measurements of the composites synthe-sized in this work show an apparent percolative behavior withpercolation threshold 119881
119862= 03 and critical exponents values
119905 = 168 and 119906 = 27 Compared to the conventionally pre-pared YBZO nanocrystalline YBZO mixed superconductor-insulator system showed a better percolation behavior Thusas discussed earlier YBZO is chemically stable with theYBCO superconductor and at the same time it did not haveany deteriorating effect on the superconducting propertycharacterized by the transition temperature
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
Acknowledgment
SukumariammaVidya acknowledgesCSIR for financial assis-tance
References
[1] T van Duzer ldquoSuperconductor electronicsrdquo Cryogenics vol 30no 12 pp 980ndash995 1990
[2] T van Duzer ldquoSuperconductor electronics and power applica-tionsrdquo Proceedings of the IEEE vol 100 no 11 pp 2993ndash29952012
[3] N McN Alford T W Button and J D Birchall ldquoProcessingproperties and devices in high-T
119888superconductorsrdquo Supercon-
ductor Science and Technology vol 3 no 1 1990[4] T K Worthington W J Gallagher and T R Dinger
ldquoAnisotropic nature of high-temperature superconductivity insingle-crystal Y
1Ba2Cu
3O7minus119909
rdquo Physical Review Letters vol 59no 10 pp 1160ndash1163 1987
[5] D R Harshman G Aeppli E J Ansaldo et al ldquoTemperaturedependence of the magnetic penetration depth in the high-T119888superconductor Ba
2YCu3O9minus120593
evidence for conventional s-wave pairingrdquo Physical Review B vol 36 no 4 pp 2386ndash23891987
[6] A Davidson and M Tinkham ldquoPhenomenological equationsfor the electrical conductivity of microscopically inhomoge-neousmaterialsrdquo Physical Review B vol 13 no 8 pp 3261ndash32671976
[7] J W Essam ldquoPercolation theoryrdquo Reports on Progress in Physicsvol 43 no 7 pp 833ndash912 1980
[8] M Sahimi Application of Percolation Theory Taylor amp FrancisLondon UK 1994
[9] K Osamura N Matsukura Y Kusumoto S Ochiai B Niand T Matsushita ldquoImprovement of critical current density inYBa2Cu3O6+119909
superconductor by Sn additionrdquo Japanese Journalof Applied Physics vol 29 no 9 pp L1621ndashL1623 1990
[10] S H Wee A Goyal Y L Zuev C Cantoni V Selvaman-ickam and E D Specht ldquoFormation of self-assembled double-perovskite Ba
2YNbO
6nanocolumns and their contribution to
flux-pinning and J119888in Nb-doped YBa2Cu3O7minus120575 filmsrdquo Applied
Physics Express vol 3 no 2 Article ID 023101 2010
International Journal of Superconductivity 7
[11] M Coll S Ye V Rouco et al ldquoSolution-derived YBa2Cu3O7minus120575
nanocomposite films with a Ba2YTaO
6secondary phase for
improved superconducting propertiesrdquo Superconductor Scienceand Technology vol 26 no 1 Article ID 015001 2012
[12] P P Rejith S Vidya S Vipinlal Solomon and J K ThomasldquoFlux-pinning properties of nanocrystalline HfO
2add
YBa2Cu3O7minus120575
superconductorrdquo Physica Status Solidi B vol 251pp 809ndash814 2014
[13] S A Harrington J H Durrell B Maiorov et al ldquorare earthtantalate pyrochlore nanoparticles for superior flux inYBa2Cu3119874
7minus120575filmsrdquo Superconductor Science and Technology
vol 22 no 2 Article ID 022001 2009[14] Y P Yadava E Montarroyos J M Ferreira and J Albino
Aguiar ldquoSynthesis and study of the structural characteristicsof a new complex perovskite oxide Sr
2HoHfO
55for its use
as a substrate for YBCO superconducting filmsrdquo Physica CSuperconductivity vol 354 no 1ndash4 pp 444ndash448 2001
[15] J Koshy J K Thomas J Kurian Y P Yadava and AD Damodaran ldquoDevelopment and characterization ofGdBa
2NbO6 a new ceramic substrate for YBCO thick filmsrdquo
Materials Letters vol 17 no 6 pp 393ndash397 1993[16] R Jose A M John J K Thomas et al ldquoSynthesis crystal
structure dielectric properties and potential use of nanocrys-talline complex perovskite ceramic oxide Ba
2ErZrO
55rdquoMateri-
als Research Bulletin vol 42 no 12 pp 1976ndash1985 2007[17] K V Paulose M T Sebastian K R Nair J Koshy and
A D Damodaran ldquoSynthesis of Ba2YZrO
6 a new phase in
YBa2Cu3O7-ZrO2system and its suitability as a substrate
material for YBCO filmsrdquo Solid State Communications vol 83no 12 pp 985ndash988 1992
[18] J M Phillips ldquoSubstrate selection for high-temperature super-conducting thin filmsrdquo Journal of Applied Physics vol 79 no 4pp 1829ndash1848 1996
[19] S Vidya K CMathai P P Rejith S Solomon and J KThomasldquoSmBa
2NbO6nanopowders an effective percolation network
medium for YBCO superconductorsrdquo Advances in MaterialsScience and Engineering vol 2013 Article ID 578434 7 pages2013
[20] J Kurian P R S Wariar P K Sajith and J Koshy ldquoPercolationbehavior of the normal-state resistivity and superconductivityof the YBa
2Cu3O7minus120575
-Ba2GdNbO
6composite systemrdquo Journal of
Superconductivity and Novel Magnetism vol 11 no 6 pp 683ndash687 1998
[21] P R S Wariar J Koshy J Kurian Y P Yadava and A DDamodaran ldquoPercolation studies in SmBa
2SbO6-YBa2Cu3O7minus120575
composite systemrdquo Modern Physics Letters B vol 9 no 10 p585 1995
[22] H Tovar O O Dıaz D A L Tellez and J Roa-RojasldquoBa2NdZrO
55as a potential substrate material for
YBa2Cu3O7minus120575
superconducting filmsrdquo Physica Status SolidiC Current Topics in Solid State Physics vol 4 no 11 pp4294ndash4297 2007
[23] O O Diaz L D Lopez Carreno J Albino Aguiar J Roa-Rojasand D A Landınez Tellez ldquotructural ordering chemical sta-bility and percolative effect analysis in YSr
2SbO6YBa2Cu3O7minus120575
complex perovskite compositesrdquo Physica C vol 408ndash410 pp886ndash888 2004
[24] Q Madueno D A Landınez Tellez and J Roa-Rojas ldquoProduc-tion and characterization of Ba
2NdSbO
6complex perovskite as
a substrate for YBa2Cu3O7minus120575
superconducting filmsrdquo ModernPhysics Letters B vol 20 p 427 2006
[25] K V Paulose M K Jayaraj J Koshy and A D DamodaranldquoPreparation and properties of Ba
2YZrO
6YBa2Cu3O7compos-
itesrdquo Solid State Communications vol 87 no 2 pp 147ndash1501993
[26] R Jose J James A M John D Sundararaman R Divakar andJ Koshy ldquoNew combustion process for nanosized YBa
2ZrO55
powdersrdquo Nanostructured Materials vol 11 no 5 pp 623ndash6291999
[27] J J Lin W Y Lin and R F Tsui ldquoElectrical transport andsuperconductivity in the Al
2O3-Bi2Sr18Ca12Cu2Oy and MgO-
Bi2Sr18Ca12Cu2O119910compositesrdquo Physica C vol 210 no 3-4 pp
455ndash462 1993[28] M Eisterer J Emhofer S Sorta M Zehetmayer and H W
Weber ldquoConnectivity and critical currents in polycrystallineMgB2rdquo Superconductor Science and Technology vol 22 no 3
Article ID 034016 2009[29] D Stauffer and A Aharony Introduction to Percolation Theory
Taylor and Francis 1994[30] J Wu and D S McLachlan ldquoPercolation exponents and thresh-
olds obtained from the nearly ideal continuum percolationsystem graphite-boron nitriderdquo Physical Review B vol 56 no3 pp 1236ndash1248 1997
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Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Solid State PhysicsJournal of
Computational Methods in Physics
Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Soft MatterJournal of
Hindawi Publishing Corporationhttpwwwhindawicom
AerodynamicsJournal of
Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
PhotonicsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Biophysics
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
ThermodynamicsJournal of
2 International Journal of Superconductivity
with the number of linkages Some cluster may become ofinfinite size at some critical density of occupied sites Abovethis critical density known as percolation threshold (119881
119904)
the infinite cluster spans entire system and the system isin percolating state For instance in an ideal mixture ofconducting and insulator particles the conductivity is zerooutside the percolating region whereas it takes a finite valueinside this region
It was reported that perovskites could be beneficialfor incorporation into YBCO due to their similar crystalstructures relative to the host YBCO phase [9] There-after perovskite based additions have gained renewed inter-est as a class of materials that can be incorporated intoREBCO superconductor for dramatic improvements in thepinning properties [10ndash13] And a number of perovskiteslike Sr
2HoHfO
55[14] GdBa
2NbO6[15] Ba
2ErZrO
55[16]
YBa2ZrO55
[17] and so forth were being considered as sub-stratematerials for YBCOfilmdepositionHowever substrateselection presents particular challenges for the productionof high-quality high-temperature superconducting (HTS)films suitable for applications [18] In order to confirm theirchemical compatibility with YBCO it is important to studythe electrical transport and percolation behavior in thesesuperconductor-insulator composites Transport propertiesand percolation behavior of high 119879
119888superconductor-metal
composites have been reported extensively [19ndash24] Thegeneral form of the double perovskites is A
2BB1015840O6 where for
the present work A = Ba B = Y and B1015840 = Zr Paulose et alstudied percolation properties of Ba
2YZrO
6prepared by con-
ventional solid state route and YBa2Cu3O7minus120575
superconductorcomposite using temperature-resistivity measurement andreported that both superconducting and normal state perco-lation threshold values of the composite are around 35 volof YBa
2Cu3O7in the system [25] In the present work the
percolation behavior and nonreactivity of nanoparticles ofYBa2ZrO55
(YBZO) ceramic prepared through an autoignit-ing combustion technique mixed with bulk YBa
2Cu3O7minus120575
(YBCO) superconductors are studied The variations in themicrostructure sintering behavior sample density electricaltransport such as 119879
119888 and current carrying capacity are also
studied
2 Materials and Methods
Conventional technique of solid state route was used forthe preparation of YBCO superconductor by which highpurity Y
2O3 BaCO
3 and CuO were thoroughly mixed in the
stoichiometric ratio of Y Ba Cu = 1 2 3 The mixture wasthen calcined at 930∘C for 72 hours with two intermediatewet grindings High quality nanoparticles of YBa
2ZrO55
(YBZO) were synthesized through modified autoignitingcombustion technique as reported by Jose et al [26] Ina typical synthesis aqueous solution containing ions of YBa and Zr was prepared by dissolving high purity Y
2O3
in dilute HNO3 Ba (NO
3)2 and ZrOCl
2(99) in double
distilled water in a glass beaker Citric acid (99) was thenadded to the solution containing Zr ions which serves asthe complexing agent Oxidantfuel ratio of the system wasadjusted by adding nitric acid and ammonium hydroxide
200nm
Figure 1 TEMmicrograph of YBa2ZrO55
nanoparticles
and the ratio was kept at unity The solution containing theprecursormixture at a pH of sim70 was heated using a hot plateatsim250∘C in a ventilated fumehoodThe combustion productwas subsequently characterized as single phase nanocrystalsof YBa
2ZrO55 The YBCO and nano-YBZO were thoroughly
mixed in different ratios and made into rectangular pelletsof dimension 12 times 4 times 1mm These pellets were sinteredat temperature ranges from 975∘C to 1500∘C for 12 hourswith a heating rate of 3∘Cminute depending on the volumepercentage of YBHO in the composite material The sampleswere then cooled to 550∘C and kept 24 hours for oxygenationand then cooled to room temperature
The structural characterization of YBCO-nanocrystallineYBZO composites was done by powder X-ray diffraction(XRD) technique using a Bruker D-8 X-ray diffractometerwithNickel filtered Cu119870
120572radiationThe surfacemorphology
of the sintered samples was studied using scanning electronmicroscopy (SEM) (JEOL JSM 6390 LV) The qualitativeand quantitative elemental composition of the materials inthe compounds was studied using energy dispersive X-rayspectroscopy (EDS) JEOLmodel JED-2300The critical tran-sition temperatures (119879
119888) of the samples were measured using
standard four-probe technique For the samples with highervol of insulator a two-probe method was used to measuretheir resistivity For this experiment the entire data collectionwas run using a Lab VIEW 71 program on a PC This wasconnected to Keithley source meter 2440 and nanovoltmeter2182A along with lakeshore temperature controller equippedwith PT-111 platinum sensor using a GPIB connection Theelectrical contacts on the surface of the pellets were doneby adhesive silver paste after making a narrow scratch onthe sample surface The self-field transport critical current(119869119888) measurements were done at liquid nitrogen temperature
using the standard 1 120583Vcm criterion
3 Results and Discussion
The powder morphology of the as-prepared YBa2ZrO55
nanopowder was done by using transmission electronmicroscopy (TEM) and is shown in Figure 1 The resultsuggested that the self-aligned nanoparticles of YBZO are ofcuboidal shape with sharp grain boundaries andwith size less
International Journal of Superconductivity 3
20 30 40 50 60 70
2120579 (deg)
(f)
(e)
(d)
(c)
(b)
(a)
Inte
nsity
(au
)
203
210
014
114
115
400 223
413
406 420
lowast220
lowast400
lowast420
lowast422
lowast440
(f)
(e)
(d)
(c)
(b)
(a)
203
210
014
114
115
400 223
413
406 420
lowastlowast220
lowast400
lowast420
lowast422
lowast440
Figure 2 XRD pattern of different vol of nano-YBZOmixed YBCO superconductor ((a) = 0 (b) = 10 (c) = 30 (d) = 50 (e) = 70and (f) = 100)
than 20 nm The selected area electron diffraction (SAED)pattern shown inset to Figure 1 reveals that the YBa
2ZrO55
nanoparticles were crystallized with bright polycrystallinediffraction rings SAED patterns were composed of a numberof bright spots arranged in concentric rings The electronswere reflected and diffracted from crystallographic planesof the unit cells of the sample to produce bright spots Therings were diffuse and hollow showing that the products werecomposed of nanocrystals with different orientations Thisis indicative of the polycrystalline nature of the crystallitesbut the spotty nature of the SAED pattern could be dueto the fact that finer crystallites with related orientationswere agglomerated together resulting in a limited set oforientations
The X-ray diffraction (XRD) patterns of composites for0ndash100 vol of nano-YBZO in the YBCO system are shownin Figure 2 XRD patterns of composites show that all thepeaks could be indexed for orthorhombic YBa
2Cu3O7minus120575
andcubic YBa
2ZrO55
and there is no extra peak detectable Thisimplies that YBa
2ZrO55
and YBa2Cu3O7minus120575
remain as twodifferent separate phases in the composite even after severeheat treatment up to 1020∘C For YBCO-YBZO compositeswith 80 vol YBZO the sintering temperature was above theperitectic temperature of YBCO (sim1030∘C) and therefore theformation of a 211 phase with YBCO is expected but in thepresent study the XRD patterns did not show the presence ofa 211 phase in the system Thus the composites synthesizedare suitable for the percolation studies
The surface morphology of the composite samples wasillustrated by scanning electron microscopy (SEM) Figure 3shows the SEM images of different vol of nano-YBZOadded YBCO composites These indicate that the surface ofthe samples presents a crystalline character which is typical ofa polycrystalline ceramic material The YBa
2Cu3O7minus120575
grainsform groups which have appearance of clusters and thereis no detectable interface interaction between the YBZOand YBCO grains However there are different grain sizes
and a random orientation of grain boundaries whereby thepresence of different intergrain conductivities is expected
The effect of YBa2ZrO55
on the superconducting tran-sition temperature 119879
119888of YBa
2Cu3O7minus120575
was studied by fourprobe measurements for temperatures ranging from 77 to300K Variation of normalized resistivity with temperatureof the YBCO superconductor mixed with different volof insulating nano-YBZO samples is shown in Figure 4It is observed that the composite sample with less than50 vol of YBCO showed a metallic behavior and gave zeroresistivity superconducting transition temperature above liq-uid nitrogen temperature However the YBCO-nano-YBZOcomposite with 80 vol of YBZO showed a conductingbehavior there is no superconducting transition up to 77KThe resistivity of composites is dominated by YBZO forvolume less than 50 of YBCO with a significant drop of120588 occurring near these values of volume The absence of asuperconducting network through the composite sample ora low vol of YBCO may be the reason for this behaviorThese results show that when YBCO is sim30 vol or abovethere are interconnected networks of superconducting grainsfor the super current to pass through the composite materialbut for lower vol of YBCO the continuous networkof superconducting grains breaks away and the resistancebecomes nearly equal to that of pure insulator Hence thevalue of percolation threshold for the YBCO-nano-YBZOcomposite sample lies between 30 and 40 vol of YBCO inthe composite
The resistivity (120588) and temperature coefficient of resis-tivity 120572 = (1120588)(119889120588119889119879) at room temperature are shownin Figure 5 as a function of vol of YBCO (119881
119878) in the
composite In the normal state YBCO behaves as a metallicconductor and shows resistivity sim10 120583Ωm However theresistivity of composites is dominated by YBa
2ZrO55
forlower vol of YBCO with a significant drop of 120588 occurringnear 30ndash50 vol The behavior of 120588 correlates with that of 120572which increases sharply towards that of YBCO starting from
4 International Journal of Superconductivity
(a) (b)
(c) (d)
(e) (f)
Figure 3 SEM images of different vol of nano-YBZO mixed YBCO superconductor ((a) = 0 (b) = 10 (c) = 30 (d) = 50 (e) = 70and (f) = 100)
119881
119878sim 30 vol So if we assumed that the electrical transport
behavior in YBCO-nano-YBZO composites is percolativethe percolation threshold 119881
119862is between 03 and 04 Thus
the superconducting percolation threshold and normal statepercolation threshold values of YBCO-nano-YBZO compos-ites lie in the same range The electrical properties of thesuperconductor-insulator system can be described in [27 28]
120588 = 120588
119900(119881
119878minus 119881
119862)
minus119905 for 119881119878gt 119881
119862
120588
1015840= 120588
1015840
119900(119881
119862minus 119881
119904)
119906 for 119881119862gt 119881
119878
(1)
where 120588119900and 1205881015840
119900are constants 119881
119862is the critical volume
fraction of superconductor at which 120588 changes dramaticallyand is called the percolation threshold 119881
119878is the vol of
superconducting material in the composite and 119905 and 119906 are
the critical exponent describing the transport properties ofthe composite system The values 120588
119900 1205881015840119900 119905 and 119906 are found
from the log-log plot of 120588 versus (119881119878minus 119881
119862) and 1205881015840 versus
(119881
119862minus 119881
119904) with 119881
119862= 03 The value of 119881
119862is adjusted so that
the log-log plots of 120588 and 1205881015840 give a straight lineLog-log plot of 120588 versus (119881
119878minus119881
119862) for119881
119878gt 119881
119862 is shown in
Figure 6 which gave the exponents 119905 = 168 and 120588119900= 508 120583Ω
m And Figure 7 shows the log-log plot of 1205881015840 in functionof (119881119862minus 119881
119904) for 119881
119862gt 119881
119878system which gave the values
119906 = 27 and 1205881015840119900= 5831 times 104 120583Ω m Least square fits were
performed to determine the slope of the plots which gavethe values of exponents 119905 and 119906 However for an idealizedmetal-insulator system 119905 = 17 and 119906 = 07 [29] A greatnumber of experiments on conducting-insulator systemsshow percolation thresholds in agreement with percolation
International Journal of Superconductivity 5N
orm
alise
d re
sistiv
ity (120588
120588r)
10
05
00
50 100 150 200 250 300
Temperature (K)
(a)
50 100 150 200 250 300
Temperature (K)
10
05
00
(b)
10
05
00
(c)
50 100 150 200 250 300
Temperature (K)
10
05
00
(d)
50 100 150 200 250 300
Temperature (K)
10
09
08
07
(e)
50 100 150 200 250 300
Temperature (K)
Figure 4 Temperature-normalised resistivity graph for differentvol of nano-YBZO mixed YBCO superconductor ((a) = 0 (b)= 20 (c) = 50 (d) = 70 and (e) = 80)
theory [19ndash21] However there are few others which reportedvariation from the universal values [27 30]
The values of critical current densities (119869119888) measured for
different samples at zero applied magnetic field are shownin Table 1 The self-field 119869
119888is found to be decreasing on
the addition of nanocrystalline YBZO in YBCO A judiciousexplanation is the existence of larger defect density since 119869
119888
is more sensitive to the defect density The analysis of thecurrent flow in the composite samples reveals the weak linkbehavior in the majority of grain connections But this doesnot necessarily mean that weak (Josephson) grain couplingis absent in these samples However the number of strongergrain connectionsmust be significantly above the percolationthreshold [28] which is defined as the minimum fraction fora continuous current path
YBa2Cu3O7minus120575
superconductor will start to melt anddecompose when it is sintered at higher temperature
40
35
30
25
20
15
10
0500 02 04 06 08 10
50
45
40
35
30
25
20
15
Vol of YBCO
Tem
pera
ture
coeffi
cien
t of r
esist
ivity
(120572)
log 120588
(120583Ω
m)
Figure 5 Variation of (a) normal state resistivity 120588 and (b)temperature coefficient of resistivity 120572 = (119897120588)(119889120588119889119879) at roomtemperature for different vol of YBCO
20
18
16
14
12
10
minus07 minus06 minus05 minus04 minus03 minus02 minus01
t = 168 1205880 = 508 120583Ωmlo
g 120588(120583Ω
m)
Vc = 03
log(VS minus VC)
Figure 6 Log-log plot of 120588 versus (119881119878minus 119881
119862)
40
38
36
34
32
30minus10 minus09 minus08 minus07
u = 27 1205889984000 = 5831 times 104 120583Ωm
log 120588
998400(120583Ω
m)
Vc = 03
log(VC minus VS)
Figure 7 Log-log plot of 120588 versus (119881119862minus 119881
119878)
6 International Journal of Superconductivity
Table 1 Sintering temperature density and electric transport data of different YBCO-nano-YBZO composites
Vol of YBCO Vol of YBZO Sintering temp (∘C) Density (gm cmminus3) 119879
119888(K) Self-field 119869
119888(times104 Acm2)
100 0 975 535 92 14790 10 983 557 92 08880 20 990 566 905 02670 30 1000 575 89 00950 50 1015 584 82 mdash30 70 1120 588 mdash mdash20 80 1230 603 mdash mdash10 90 1370 615 mdash mdash0 100 1500 627 mdash mdash
The values of 119881119862 119905 and 119906 obtained for different systems
of composites vary due to many factors The critical expo-nents 119905 and 119906 are a measure of the order of interactionbetween normal metal and insulator The value for idealpercolation threshold is around 17 vol of metal in thesystem for a perfect metal-insulator composite without anyinteraction or reaction between the two The normal stateand superconducting percolation threshold values of YBCO-nano-YBZO (03 vol of YBCO) composites are in closerranges as expected for an idealized percolation system and arelower than those observed in conventionally preparedYBZO-YBCO (035 vol of YBCO) composite [25] This may bedue to the better chemical nonreactivity between YBCO andnano-YBZO Furthermore there is a negligible conductivitybelow percolation threshold while it is expected to be zeroin ideal percolative systemsThe nonreactivity of YBCOwithnano-YBZO even at high processing temperature also pointsto the fact that nano-YBZO is a suitable substrate for YBCOsuperconductor and thus to develop devices based on hightemperature superconductor films and junctions
4 Conclusion
In this paper we have studied the chemical reactivityand percolation behavior using electric transport mea-surements in polycrystalline YBa
2Cu3O7minus120575
superconductor-nano-YBa
2ZrO55
composite From structural analysis it isobserved that the mixture of materials YBa
2ZrO55
insulatorwith YBa
2Cu3O7minus120575
superconductor is a system where theparticles of superconductor and insulator materials are foundto coexist in a composite with two well-defined separatephases Resistivity measurements of the composites synthe-sized in this work show an apparent percolative behavior withpercolation threshold 119881
119862= 03 and critical exponents values
119905 = 168 and 119906 = 27 Compared to the conventionally pre-pared YBZO nanocrystalline YBZO mixed superconductor-insulator system showed a better percolation behavior Thusas discussed earlier YBZO is chemically stable with theYBCO superconductor and at the same time it did not haveany deteriorating effect on the superconducting propertycharacterized by the transition temperature
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
Acknowledgment
SukumariammaVidya acknowledgesCSIR for financial assis-tance
References
[1] T van Duzer ldquoSuperconductor electronicsrdquo Cryogenics vol 30no 12 pp 980ndash995 1990
[2] T van Duzer ldquoSuperconductor electronics and power applica-tionsrdquo Proceedings of the IEEE vol 100 no 11 pp 2993ndash29952012
[3] N McN Alford T W Button and J D Birchall ldquoProcessingproperties and devices in high-T
119888superconductorsrdquo Supercon-
ductor Science and Technology vol 3 no 1 1990[4] T K Worthington W J Gallagher and T R Dinger
ldquoAnisotropic nature of high-temperature superconductivity insingle-crystal Y
1Ba2Cu
3O7minus119909
rdquo Physical Review Letters vol 59no 10 pp 1160ndash1163 1987
[5] D R Harshman G Aeppli E J Ansaldo et al ldquoTemperaturedependence of the magnetic penetration depth in the high-T119888superconductor Ba
2YCu3O9minus120593
evidence for conventional s-wave pairingrdquo Physical Review B vol 36 no 4 pp 2386ndash23891987
[6] A Davidson and M Tinkham ldquoPhenomenological equationsfor the electrical conductivity of microscopically inhomoge-neousmaterialsrdquo Physical Review B vol 13 no 8 pp 3261ndash32671976
[7] J W Essam ldquoPercolation theoryrdquo Reports on Progress in Physicsvol 43 no 7 pp 833ndash912 1980
[8] M Sahimi Application of Percolation Theory Taylor amp FrancisLondon UK 1994
[9] K Osamura N Matsukura Y Kusumoto S Ochiai B Niand T Matsushita ldquoImprovement of critical current density inYBa2Cu3O6+119909
superconductor by Sn additionrdquo Japanese Journalof Applied Physics vol 29 no 9 pp L1621ndashL1623 1990
[10] S H Wee A Goyal Y L Zuev C Cantoni V Selvaman-ickam and E D Specht ldquoFormation of self-assembled double-perovskite Ba
2YNbO
6nanocolumns and their contribution to
flux-pinning and J119888in Nb-doped YBa2Cu3O7minus120575 filmsrdquo Applied
Physics Express vol 3 no 2 Article ID 023101 2010
International Journal of Superconductivity 7
[11] M Coll S Ye V Rouco et al ldquoSolution-derived YBa2Cu3O7minus120575
nanocomposite films with a Ba2YTaO
6secondary phase for
improved superconducting propertiesrdquo Superconductor Scienceand Technology vol 26 no 1 Article ID 015001 2012
[12] P P Rejith S Vidya S Vipinlal Solomon and J K ThomasldquoFlux-pinning properties of nanocrystalline HfO
2add
YBa2Cu3O7minus120575
superconductorrdquo Physica Status Solidi B vol 251pp 809ndash814 2014
[13] S A Harrington J H Durrell B Maiorov et al ldquorare earthtantalate pyrochlore nanoparticles for superior flux inYBa2Cu3119874
7minus120575filmsrdquo Superconductor Science and Technology
vol 22 no 2 Article ID 022001 2009[14] Y P Yadava E Montarroyos J M Ferreira and J Albino
Aguiar ldquoSynthesis and study of the structural characteristicsof a new complex perovskite oxide Sr
2HoHfO
55for its use
as a substrate for YBCO superconducting filmsrdquo Physica CSuperconductivity vol 354 no 1ndash4 pp 444ndash448 2001
[15] J Koshy J K Thomas J Kurian Y P Yadava and AD Damodaran ldquoDevelopment and characterization ofGdBa
2NbO6 a new ceramic substrate for YBCO thick filmsrdquo
Materials Letters vol 17 no 6 pp 393ndash397 1993[16] R Jose A M John J K Thomas et al ldquoSynthesis crystal
structure dielectric properties and potential use of nanocrys-talline complex perovskite ceramic oxide Ba
2ErZrO
55rdquoMateri-
als Research Bulletin vol 42 no 12 pp 1976ndash1985 2007[17] K V Paulose M T Sebastian K R Nair J Koshy and
A D Damodaran ldquoSynthesis of Ba2YZrO
6 a new phase in
YBa2Cu3O7-ZrO2system and its suitability as a substrate
material for YBCO filmsrdquo Solid State Communications vol 83no 12 pp 985ndash988 1992
[18] J M Phillips ldquoSubstrate selection for high-temperature super-conducting thin filmsrdquo Journal of Applied Physics vol 79 no 4pp 1829ndash1848 1996
[19] S Vidya K CMathai P P Rejith S Solomon and J KThomasldquoSmBa
2NbO6nanopowders an effective percolation network
medium for YBCO superconductorsrdquo Advances in MaterialsScience and Engineering vol 2013 Article ID 578434 7 pages2013
[20] J Kurian P R S Wariar P K Sajith and J Koshy ldquoPercolationbehavior of the normal-state resistivity and superconductivityof the YBa
2Cu3O7minus120575
-Ba2GdNbO
6composite systemrdquo Journal of
Superconductivity and Novel Magnetism vol 11 no 6 pp 683ndash687 1998
[21] P R S Wariar J Koshy J Kurian Y P Yadava and A DDamodaran ldquoPercolation studies in SmBa
2SbO6-YBa2Cu3O7minus120575
composite systemrdquo Modern Physics Letters B vol 9 no 10 p585 1995
[22] H Tovar O O Dıaz D A L Tellez and J Roa-RojasldquoBa2NdZrO
55as a potential substrate material for
YBa2Cu3O7minus120575
superconducting filmsrdquo Physica Status SolidiC Current Topics in Solid State Physics vol 4 no 11 pp4294ndash4297 2007
[23] O O Diaz L D Lopez Carreno J Albino Aguiar J Roa-Rojasand D A Landınez Tellez ldquotructural ordering chemical sta-bility and percolative effect analysis in YSr
2SbO6YBa2Cu3O7minus120575
complex perovskite compositesrdquo Physica C vol 408ndash410 pp886ndash888 2004
[24] Q Madueno D A Landınez Tellez and J Roa-Rojas ldquoProduc-tion and characterization of Ba
2NdSbO
6complex perovskite as
a substrate for YBa2Cu3O7minus120575
superconducting filmsrdquo ModernPhysics Letters B vol 20 p 427 2006
[25] K V Paulose M K Jayaraj J Koshy and A D DamodaranldquoPreparation and properties of Ba
2YZrO
6YBa2Cu3O7compos-
itesrdquo Solid State Communications vol 87 no 2 pp 147ndash1501993
[26] R Jose J James A M John D Sundararaman R Divakar andJ Koshy ldquoNew combustion process for nanosized YBa
2ZrO55
powdersrdquo Nanostructured Materials vol 11 no 5 pp 623ndash6291999
[27] J J Lin W Y Lin and R F Tsui ldquoElectrical transport andsuperconductivity in the Al
2O3-Bi2Sr18Ca12Cu2Oy and MgO-
Bi2Sr18Ca12Cu2O119910compositesrdquo Physica C vol 210 no 3-4 pp
455ndash462 1993[28] M Eisterer J Emhofer S Sorta M Zehetmayer and H W
Weber ldquoConnectivity and critical currents in polycrystallineMgB2rdquo Superconductor Science and Technology vol 22 no 3
Article ID 034016 2009[29] D Stauffer and A Aharony Introduction to Percolation Theory
Taylor and Francis 1994[30] J Wu and D S McLachlan ldquoPercolation exponents and thresh-
olds obtained from the nearly ideal continuum percolationsystem graphite-boron nitriderdquo Physical Review B vol 56 no3 pp 1236ndash1248 1997
Submit your manuscripts athttpwwwhindawicom
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
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Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Superconductivity
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Statistical MechanicsInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
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Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
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Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Solid State PhysicsJournal of
Computational Methods in Physics
Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Soft MatterJournal of
Hindawi Publishing Corporationhttpwwwhindawicom
AerodynamicsJournal of
Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
PhotonicsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Biophysics
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
ThermodynamicsJournal of
International Journal of Superconductivity 3
20 30 40 50 60 70
2120579 (deg)
(f)
(e)
(d)
(c)
(b)
(a)
Inte
nsity
(au
)
203
210
014
114
115
400 223
413
406 420
lowast220
lowast400
lowast420
lowast422
lowast440
(f)
(e)
(d)
(c)
(b)
(a)
203
210
014
114
115
400 223
413
406 420
lowastlowast220
lowast400
lowast420
lowast422
lowast440
Figure 2 XRD pattern of different vol of nano-YBZOmixed YBCO superconductor ((a) = 0 (b) = 10 (c) = 30 (d) = 50 (e) = 70and (f) = 100)
than 20 nm The selected area electron diffraction (SAED)pattern shown inset to Figure 1 reveals that the YBa
2ZrO55
nanoparticles were crystallized with bright polycrystallinediffraction rings SAED patterns were composed of a numberof bright spots arranged in concentric rings The electronswere reflected and diffracted from crystallographic planesof the unit cells of the sample to produce bright spots Therings were diffuse and hollow showing that the products werecomposed of nanocrystals with different orientations Thisis indicative of the polycrystalline nature of the crystallitesbut the spotty nature of the SAED pattern could be dueto the fact that finer crystallites with related orientationswere agglomerated together resulting in a limited set oforientations
The X-ray diffraction (XRD) patterns of composites for0ndash100 vol of nano-YBZO in the YBCO system are shownin Figure 2 XRD patterns of composites show that all thepeaks could be indexed for orthorhombic YBa
2Cu3O7minus120575
andcubic YBa
2ZrO55
and there is no extra peak detectable Thisimplies that YBa
2ZrO55
and YBa2Cu3O7minus120575
remain as twodifferent separate phases in the composite even after severeheat treatment up to 1020∘C For YBCO-YBZO compositeswith 80 vol YBZO the sintering temperature was above theperitectic temperature of YBCO (sim1030∘C) and therefore theformation of a 211 phase with YBCO is expected but in thepresent study the XRD patterns did not show the presence ofa 211 phase in the system Thus the composites synthesizedare suitable for the percolation studies
The surface morphology of the composite samples wasillustrated by scanning electron microscopy (SEM) Figure 3shows the SEM images of different vol of nano-YBZOadded YBCO composites These indicate that the surface ofthe samples presents a crystalline character which is typical ofa polycrystalline ceramic material The YBa
2Cu3O7minus120575
grainsform groups which have appearance of clusters and thereis no detectable interface interaction between the YBZOand YBCO grains However there are different grain sizes
and a random orientation of grain boundaries whereby thepresence of different intergrain conductivities is expected
The effect of YBa2ZrO55
on the superconducting tran-sition temperature 119879
119888of YBa
2Cu3O7minus120575
was studied by fourprobe measurements for temperatures ranging from 77 to300K Variation of normalized resistivity with temperatureof the YBCO superconductor mixed with different volof insulating nano-YBZO samples is shown in Figure 4It is observed that the composite sample with less than50 vol of YBCO showed a metallic behavior and gave zeroresistivity superconducting transition temperature above liq-uid nitrogen temperature However the YBCO-nano-YBZOcomposite with 80 vol of YBZO showed a conductingbehavior there is no superconducting transition up to 77KThe resistivity of composites is dominated by YBZO forvolume less than 50 of YBCO with a significant drop of120588 occurring near these values of volume The absence of asuperconducting network through the composite sample ora low vol of YBCO may be the reason for this behaviorThese results show that when YBCO is sim30 vol or abovethere are interconnected networks of superconducting grainsfor the super current to pass through the composite materialbut for lower vol of YBCO the continuous networkof superconducting grains breaks away and the resistancebecomes nearly equal to that of pure insulator Hence thevalue of percolation threshold for the YBCO-nano-YBZOcomposite sample lies between 30 and 40 vol of YBCO inthe composite
The resistivity (120588) and temperature coefficient of resis-tivity 120572 = (1120588)(119889120588119889119879) at room temperature are shownin Figure 5 as a function of vol of YBCO (119881
119878) in the
composite In the normal state YBCO behaves as a metallicconductor and shows resistivity sim10 120583Ωm However theresistivity of composites is dominated by YBa
2ZrO55
forlower vol of YBCO with a significant drop of 120588 occurringnear 30ndash50 vol The behavior of 120588 correlates with that of 120572which increases sharply towards that of YBCO starting from
4 International Journal of Superconductivity
(a) (b)
(c) (d)
(e) (f)
Figure 3 SEM images of different vol of nano-YBZO mixed YBCO superconductor ((a) = 0 (b) = 10 (c) = 30 (d) = 50 (e) = 70and (f) = 100)
119881
119878sim 30 vol So if we assumed that the electrical transport
behavior in YBCO-nano-YBZO composites is percolativethe percolation threshold 119881
119862is between 03 and 04 Thus
the superconducting percolation threshold and normal statepercolation threshold values of YBCO-nano-YBZO compos-ites lie in the same range The electrical properties of thesuperconductor-insulator system can be described in [27 28]
120588 = 120588
119900(119881
119878minus 119881
119862)
minus119905 for 119881119878gt 119881
119862
120588
1015840= 120588
1015840
119900(119881
119862minus 119881
119904)
119906 for 119881119862gt 119881
119878
(1)
where 120588119900and 1205881015840
119900are constants 119881
119862is the critical volume
fraction of superconductor at which 120588 changes dramaticallyand is called the percolation threshold 119881
119878is the vol of
superconducting material in the composite and 119905 and 119906 are
the critical exponent describing the transport properties ofthe composite system The values 120588
119900 1205881015840119900 119905 and 119906 are found
from the log-log plot of 120588 versus (119881119878minus 119881
119862) and 1205881015840 versus
(119881
119862minus 119881
119904) with 119881
119862= 03 The value of 119881
119862is adjusted so that
the log-log plots of 120588 and 1205881015840 give a straight lineLog-log plot of 120588 versus (119881
119878minus119881
119862) for119881
119878gt 119881
119862 is shown in
Figure 6 which gave the exponents 119905 = 168 and 120588119900= 508 120583Ω
m And Figure 7 shows the log-log plot of 1205881015840 in functionof (119881119862minus 119881
119904) for 119881
119862gt 119881
119878system which gave the values
119906 = 27 and 1205881015840119900= 5831 times 104 120583Ω m Least square fits were
performed to determine the slope of the plots which gavethe values of exponents 119905 and 119906 However for an idealizedmetal-insulator system 119905 = 17 and 119906 = 07 [29] A greatnumber of experiments on conducting-insulator systemsshow percolation thresholds in agreement with percolation
International Journal of Superconductivity 5N
orm
alise
d re
sistiv
ity (120588
120588r)
10
05
00
50 100 150 200 250 300
Temperature (K)
(a)
50 100 150 200 250 300
Temperature (K)
10
05
00
(b)
10
05
00
(c)
50 100 150 200 250 300
Temperature (K)
10
05
00
(d)
50 100 150 200 250 300
Temperature (K)
10
09
08
07
(e)
50 100 150 200 250 300
Temperature (K)
Figure 4 Temperature-normalised resistivity graph for differentvol of nano-YBZO mixed YBCO superconductor ((a) = 0 (b)= 20 (c) = 50 (d) = 70 and (e) = 80)
theory [19ndash21] However there are few others which reportedvariation from the universal values [27 30]
The values of critical current densities (119869119888) measured for
different samples at zero applied magnetic field are shownin Table 1 The self-field 119869
119888is found to be decreasing on
the addition of nanocrystalline YBZO in YBCO A judiciousexplanation is the existence of larger defect density since 119869
119888
is more sensitive to the defect density The analysis of thecurrent flow in the composite samples reveals the weak linkbehavior in the majority of grain connections But this doesnot necessarily mean that weak (Josephson) grain couplingis absent in these samples However the number of strongergrain connectionsmust be significantly above the percolationthreshold [28] which is defined as the minimum fraction fora continuous current path
YBa2Cu3O7minus120575
superconductor will start to melt anddecompose when it is sintered at higher temperature
40
35
30
25
20
15
10
0500 02 04 06 08 10
50
45
40
35
30
25
20
15
Vol of YBCO
Tem
pera
ture
coeffi
cien
t of r
esist
ivity
(120572)
log 120588
(120583Ω
m)
Figure 5 Variation of (a) normal state resistivity 120588 and (b)temperature coefficient of resistivity 120572 = (119897120588)(119889120588119889119879) at roomtemperature for different vol of YBCO
20
18
16
14
12
10
minus07 minus06 minus05 minus04 minus03 minus02 minus01
t = 168 1205880 = 508 120583Ωmlo
g 120588(120583Ω
m)
Vc = 03
log(VS minus VC)
Figure 6 Log-log plot of 120588 versus (119881119878minus 119881
119862)
40
38
36
34
32
30minus10 minus09 minus08 minus07
u = 27 1205889984000 = 5831 times 104 120583Ωm
log 120588
998400(120583Ω
m)
Vc = 03
log(VC minus VS)
Figure 7 Log-log plot of 120588 versus (119881119862minus 119881
119878)
6 International Journal of Superconductivity
Table 1 Sintering temperature density and electric transport data of different YBCO-nano-YBZO composites
Vol of YBCO Vol of YBZO Sintering temp (∘C) Density (gm cmminus3) 119879
119888(K) Self-field 119869
119888(times104 Acm2)
100 0 975 535 92 14790 10 983 557 92 08880 20 990 566 905 02670 30 1000 575 89 00950 50 1015 584 82 mdash30 70 1120 588 mdash mdash20 80 1230 603 mdash mdash10 90 1370 615 mdash mdash0 100 1500 627 mdash mdash
The values of 119881119862 119905 and 119906 obtained for different systems
of composites vary due to many factors The critical expo-nents 119905 and 119906 are a measure of the order of interactionbetween normal metal and insulator The value for idealpercolation threshold is around 17 vol of metal in thesystem for a perfect metal-insulator composite without anyinteraction or reaction between the two The normal stateand superconducting percolation threshold values of YBCO-nano-YBZO (03 vol of YBCO) composites are in closerranges as expected for an idealized percolation system and arelower than those observed in conventionally preparedYBZO-YBCO (035 vol of YBCO) composite [25] This may bedue to the better chemical nonreactivity between YBCO andnano-YBZO Furthermore there is a negligible conductivitybelow percolation threshold while it is expected to be zeroin ideal percolative systemsThe nonreactivity of YBCOwithnano-YBZO even at high processing temperature also pointsto the fact that nano-YBZO is a suitable substrate for YBCOsuperconductor and thus to develop devices based on hightemperature superconductor films and junctions
4 Conclusion
In this paper we have studied the chemical reactivityand percolation behavior using electric transport mea-surements in polycrystalline YBa
2Cu3O7minus120575
superconductor-nano-YBa
2ZrO55
composite From structural analysis it isobserved that the mixture of materials YBa
2ZrO55
insulatorwith YBa
2Cu3O7minus120575
superconductor is a system where theparticles of superconductor and insulator materials are foundto coexist in a composite with two well-defined separatephases Resistivity measurements of the composites synthe-sized in this work show an apparent percolative behavior withpercolation threshold 119881
119862= 03 and critical exponents values
119905 = 168 and 119906 = 27 Compared to the conventionally pre-pared YBZO nanocrystalline YBZO mixed superconductor-insulator system showed a better percolation behavior Thusas discussed earlier YBZO is chemically stable with theYBCO superconductor and at the same time it did not haveany deteriorating effect on the superconducting propertycharacterized by the transition temperature
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
Acknowledgment
SukumariammaVidya acknowledgesCSIR for financial assis-tance
References
[1] T van Duzer ldquoSuperconductor electronicsrdquo Cryogenics vol 30no 12 pp 980ndash995 1990
[2] T van Duzer ldquoSuperconductor electronics and power applica-tionsrdquo Proceedings of the IEEE vol 100 no 11 pp 2993ndash29952012
[3] N McN Alford T W Button and J D Birchall ldquoProcessingproperties and devices in high-T
119888superconductorsrdquo Supercon-
ductor Science and Technology vol 3 no 1 1990[4] T K Worthington W J Gallagher and T R Dinger
ldquoAnisotropic nature of high-temperature superconductivity insingle-crystal Y
1Ba2Cu
3O7minus119909
rdquo Physical Review Letters vol 59no 10 pp 1160ndash1163 1987
[5] D R Harshman G Aeppli E J Ansaldo et al ldquoTemperaturedependence of the magnetic penetration depth in the high-T119888superconductor Ba
2YCu3O9minus120593
evidence for conventional s-wave pairingrdquo Physical Review B vol 36 no 4 pp 2386ndash23891987
[6] A Davidson and M Tinkham ldquoPhenomenological equationsfor the electrical conductivity of microscopically inhomoge-neousmaterialsrdquo Physical Review B vol 13 no 8 pp 3261ndash32671976
[7] J W Essam ldquoPercolation theoryrdquo Reports on Progress in Physicsvol 43 no 7 pp 833ndash912 1980
[8] M Sahimi Application of Percolation Theory Taylor amp FrancisLondon UK 1994
[9] K Osamura N Matsukura Y Kusumoto S Ochiai B Niand T Matsushita ldquoImprovement of critical current density inYBa2Cu3O6+119909
superconductor by Sn additionrdquo Japanese Journalof Applied Physics vol 29 no 9 pp L1621ndashL1623 1990
[10] S H Wee A Goyal Y L Zuev C Cantoni V Selvaman-ickam and E D Specht ldquoFormation of self-assembled double-perovskite Ba
2YNbO
6nanocolumns and their contribution to
flux-pinning and J119888in Nb-doped YBa2Cu3O7minus120575 filmsrdquo Applied
Physics Express vol 3 no 2 Article ID 023101 2010
International Journal of Superconductivity 7
[11] M Coll S Ye V Rouco et al ldquoSolution-derived YBa2Cu3O7minus120575
nanocomposite films with a Ba2YTaO
6secondary phase for
improved superconducting propertiesrdquo Superconductor Scienceand Technology vol 26 no 1 Article ID 015001 2012
[12] P P Rejith S Vidya S Vipinlal Solomon and J K ThomasldquoFlux-pinning properties of nanocrystalline HfO
2add
YBa2Cu3O7minus120575
superconductorrdquo Physica Status Solidi B vol 251pp 809ndash814 2014
[13] S A Harrington J H Durrell B Maiorov et al ldquorare earthtantalate pyrochlore nanoparticles for superior flux inYBa2Cu3119874
7minus120575filmsrdquo Superconductor Science and Technology
vol 22 no 2 Article ID 022001 2009[14] Y P Yadava E Montarroyos J M Ferreira and J Albino
Aguiar ldquoSynthesis and study of the structural characteristicsof a new complex perovskite oxide Sr
2HoHfO
55for its use
as a substrate for YBCO superconducting filmsrdquo Physica CSuperconductivity vol 354 no 1ndash4 pp 444ndash448 2001
[15] J Koshy J K Thomas J Kurian Y P Yadava and AD Damodaran ldquoDevelopment and characterization ofGdBa
2NbO6 a new ceramic substrate for YBCO thick filmsrdquo
Materials Letters vol 17 no 6 pp 393ndash397 1993[16] R Jose A M John J K Thomas et al ldquoSynthesis crystal
structure dielectric properties and potential use of nanocrys-talline complex perovskite ceramic oxide Ba
2ErZrO
55rdquoMateri-
als Research Bulletin vol 42 no 12 pp 1976ndash1985 2007[17] K V Paulose M T Sebastian K R Nair J Koshy and
A D Damodaran ldquoSynthesis of Ba2YZrO
6 a new phase in
YBa2Cu3O7-ZrO2system and its suitability as a substrate
material for YBCO filmsrdquo Solid State Communications vol 83no 12 pp 985ndash988 1992
[18] J M Phillips ldquoSubstrate selection for high-temperature super-conducting thin filmsrdquo Journal of Applied Physics vol 79 no 4pp 1829ndash1848 1996
[19] S Vidya K CMathai P P Rejith S Solomon and J KThomasldquoSmBa
2NbO6nanopowders an effective percolation network
medium for YBCO superconductorsrdquo Advances in MaterialsScience and Engineering vol 2013 Article ID 578434 7 pages2013
[20] J Kurian P R S Wariar P K Sajith and J Koshy ldquoPercolationbehavior of the normal-state resistivity and superconductivityof the YBa
2Cu3O7minus120575
-Ba2GdNbO
6composite systemrdquo Journal of
Superconductivity and Novel Magnetism vol 11 no 6 pp 683ndash687 1998
[21] P R S Wariar J Koshy J Kurian Y P Yadava and A DDamodaran ldquoPercolation studies in SmBa
2SbO6-YBa2Cu3O7minus120575
composite systemrdquo Modern Physics Letters B vol 9 no 10 p585 1995
[22] H Tovar O O Dıaz D A L Tellez and J Roa-RojasldquoBa2NdZrO
55as a potential substrate material for
YBa2Cu3O7minus120575
superconducting filmsrdquo Physica Status SolidiC Current Topics in Solid State Physics vol 4 no 11 pp4294ndash4297 2007
[23] O O Diaz L D Lopez Carreno J Albino Aguiar J Roa-Rojasand D A Landınez Tellez ldquotructural ordering chemical sta-bility and percolative effect analysis in YSr
2SbO6YBa2Cu3O7minus120575
complex perovskite compositesrdquo Physica C vol 408ndash410 pp886ndash888 2004
[24] Q Madueno D A Landınez Tellez and J Roa-Rojas ldquoProduc-tion and characterization of Ba
2NdSbO
6complex perovskite as
a substrate for YBa2Cu3O7minus120575
superconducting filmsrdquo ModernPhysics Letters B vol 20 p 427 2006
[25] K V Paulose M K Jayaraj J Koshy and A D DamodaranldquoPreparation and properties of Ba
2YZrO
6YBa2Cu3O7compos-
itesrdquo Solid State Communications vol 87 no 2 pp 147ndash1501993
[26] R Jose J James A M John D Sundararaman R Divakar andJ Koshy ldquoNew combustion process for nanosized YBa
2ZrO55
powdersrdquo Nanostructured Materials vol 11 no 5 pp 623ndash6291999
[27] J J Lin W Y Lin and R F Tsui ldquoElectrical transport andsuperconductivity in the Al
2O3-Bi2Sr18Ca12Cu2Oy and MgO-
Bi2Sr18Ca12Cu2O119910compositesrdquo Physica C vol 210 no 3-4 pp
455ndash462 1993[28] M Eisterer J Emhofer S Sorta M Zehetmayer and H W
Weber ldquoConnectivity and critical currents in polycrystallineMgB2rdquo Superconductor Science and Technology vol 22 no 3
Article ID 034016 2009[29] D Stauffer and A Aharony Introduction to Percolation Theory
Taylor and Francis 1994[30] J Wu and D S McLachlan ldquoPercolation exponents and thresh-
olds obtained from the nearly ideal continuum percolationsystem graphite-boron nitriderdquo Physical Review B vol 56 no3 pp 1236ndash1248 1997
Submit your manuscripts athttpwwwhindawicom
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
High Energy PhysicsAdvances in
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
FluidsJournal of
Atomic and Molecular Physics
Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Advances in Condensed Matter Physics
OpticsInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
AstronomyAdvances in
International Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Superconductivity
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Statistical MechanicsInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
GravityJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
AstrophysicsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Physics Research International
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Solid State PhysicsJournal of
Computational Methods in Physics
Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Soft MatterJournal of
Hindawi Publishing Corporationhttpwwwhindawicom
AerodynamicsJournal of
Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
PhotonicsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Biophysics
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
ThermodynamicsJournal of
4 International Journal of Superconductivity
(a) (b)
(c) (d)
(e) (f)
Figure 3 SEM images of different vol of nano-YBZO mixed YBCO superconductor ((a) = 0 (b) = 10 (c) = 30 (d) = 50 (e) = 70and (f) = 100)
119881
119878sim 30 vol So if we assumed that the electrical transport
behavior in YBCO-nano-YBZO composites is percolativethe percolation threshold 119881
119862is between 03 and 04 Thus
the superconducting percolation threshold and normal statepercolation threshold values of YBCO-nano-YBZO compos-ites lie in the same range The electrical properties of thesuperconductor-insulator system can be described in [27 28]
120588 = 120588
119900(119881
119878minus 119881
119862)
minus119905 for 119881119878gt 119881
119862
120588
1015840= 120588
1015840
119900(119881
119862minus 119881
119904)
119906 for 119881119862gt 119881
119878
(1)
where 120588119900and 1205881015840
119900are constants 119881
119862is the critical volume
fraction of superconductor at which 120588 changes dramaticallyand is called the percolation threshold 119881
119878is the vol of
superconducting material in the composite and 119905 and 119906 are
the critical exponent describing the transport properties ofthe composite system The values 120588
119900 1205881015840119900 119905 and 119906 are found
from the log-log plot of 120588 versus (119881119878minus 119881
119862) and 1205881015840 versus
(119881
119862minus 119881
119904) with 119881
119862= 03 The value of 119881
119862is adjusted so that
the log-log plots of 120588 and 1205881015840 give a straight lineLog-log plot of 120588 versus (119881
119878minus119881
119862) for119881
119878gt 119881
119862 is shown in
Figure 6 which gave the exponents 119905 = 168 and 120588119900= 508 120583Ω
m And Figure 7 shows the log-log plot of 1205881015840 in functionof (119881119862minus 119881
119904) for 119881
119862gt 119881
119878system which gave the values
119906 = 27 and 1205881015840119900= 5831 times 104 120583Ω m Least square fits were
performed to determine the slope of the plots which gavethe values of exponents 119905 and 119906 However for an idealizedmetal-insulator system 119905 = 17 and 119906 = 07 [29] A greatnumber of experiments on conducting-insulator systemsshow percolation thresholds in agreement with percolation
International Journal of Superconductivity 5N
orm
alise
d re
sistiv
ity (120588
120588r)
10
05
00
50 100 150 200 250 300
Temperature (K)
(a)
50 100 150 200 250 300
Temperature (K)
10
05
00
(b)
10
05
00
(c)
50 100 150 200 250 300
Temperature (K)
10
05
00
(d)
50 100 150 200 250 300
Temperature (K)
10
09
08
07
(e)
50 100 150 200 250 300
Temperature (K)
Figure 4 Temperature-normalised resistivity graph for differentvol of nano-YBZO mixed YBCO superconductor ((a) = 0 (b)= 20 (c) = 50 (d) = 70 and (e) = 80)
theory [19ndash21] However there are few others which reportedvariation from the universal values [27 30]
The values of critical current densities (119869119888) measured for
different samples at zero applied magnetic field are shownin Table 1 The self-field 119869
119888is found to be decreasing on
the addition of nanocrystalline YBZO in YBCO A judiciousexplanation is the existence of larger defect density since 119869
119888
is more sensitive to the defect density The analysis of thecurrent flow in the composite samples reveals the weak linkbehavior in the majority of grain connections But this doesnot necessarily mean that weak (Josephson) grain couplingis absent in these samples However the number of strongergrain connectionsmust be significantly above the percolationthreshold [28] which is defined as the minimum fraction fora continuous current path
YBa2Cu3O7minus120575
superconductor will start to melt anddecompose when it is sintered at higher temperature
40
35
30
25
20
15
10
0500 02 04 06 08 10
50
45
40
35
30
25
20
15
Vol of YBCO
Tem
pera
ture
coeffi
cien
t of r
esist
ivity
(120572)
log 120588
(120583Ω
m)
Figure 5 Variation of (a) normal state resistivity 120588 and (b)temperature coefficient of resistivity 120572 = (119897120588)(119889120588119889119879) at roomtemperature for different vol of YBCO
20
18
16
14
12
10
minus07 minus06 minus05 minus04 minus03 minus02 minus01
t = 168 1205880 = 508 120583Ωmlo
g 120588(120583Ω
m)
Vc = 03
log(VS minus VC)
Figure 6 Log-log plot of 120588 versus (119881119878minus 119881
119862)
40
38
36
34
32
30minus10 minus09 minus08 minus07
u = 27 1205889984000 = 5831 times 104 120583Ωm
log 120588
998400(120583Ω
m)
Vc = 03
log(VC minus VS)
Figure 7 Log-log plot of 120588 versus (119881119862minus 119881
119878)
6 International Journal of Superconductivity
Table 1 Sintering temperature density and electric transport data of different YBCO-nano-YBZO composites
Vol of YBCO Vol of YBZO Sintering temp (∘C) Density (gm cmminus3) 119879
119888(K) Self-field 119869
119888(times104 Acm2)
100 0 975 535 92 14790 10 983 557 92 08880 20 990 566 905 02670 30 1000 575 89 00950 50 1015 584 82 mdash30 70 1120 588 mdash mdash20 80 1230 603 mdash mdash10 90 1370 615 mdash mdash0 100 1500 627 mdash mdash
The values of 119881119862 119905 and 119906 obtained for different systems
of composites vary due to many factors The critical expo-nents 119905 and 119906 are a measure of the order of interactionbetween normal metal and insulator The value for idealpercolation threshold is around 17 vol of metal in thesystem for a perfect metal-insulator composite without anyinteraction or reaction between the two The normal stateand superconducting percolation threshold values of YBCO-nano-YBZO (03 vol of YBCO) composites are in closerranges as expected for an idealized percolation system and arelower than those observed in conventionally preparedYBZO-YBCO (035 vol of YBCO) composite [25] This may bedue to the better chemical nonreactivity between YBCO andnano-YBZO Furthermore there is a negligible conductivitybelow percolation threshold while it is expected to be zeroin ideal percolative systemsThe nonreactivity of YBCOwithnano-YBZO even at high processing temperature also pointsto the fact that nano-YBZO is a suitable substrate for YBCOsuperconductor and thus to develop devices based on hightemperature superconductor films and junctions
4 Conclusion
In this paper we have studied the chemical reactivityand percolation behavior using electric transport mea-surements in polycrystalline YBa
2Cu3O7minus120575
superconductor-nano-YBa
2ZrO55
composite From structural analysis it isobserved that the mixture of materials YBa
2ZrO55
insulatorwith YBa
2Cu3O7minus120575
superconductor is a system where theparticles of superconductor and insulator materials are foundto coexist in a composite with two well-defined separatephases Resistivity measurements of the composites synthe-sized in this work show an apparent percolative behavior withpercolation threshold 119881
119862= 03 and critical exponents values
119905 = 168 and 119906 = 27 Compared to the conventionally pre-pared YBZO nanocrystalline YBZO mixed superconductor-insulator system showed a better percolation behavior Thusas discussed earlier YBZO is chemically stable with theYBCO superconductor and at the same time it did not haveany deteriorating effect on the superconducting propertycharacterized by the transition temperature
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
Acknowledgment
SukumariammaVidya acknowledgesCSIR for financial assis-tance
References
[1] T van Duzer ldquoSuperconductor electronicsrdquo Cryogenics vol 30no 12 pp 980ndash995 1990
[2] T van Duzer ldquoSuperconductor electronics and power applica-tionsrdquo Proceedings of the IEEE vol 100 no 11 pp 2993ndash29952012
[3] N McN Alford T W Button and J D Birchall ldquoProcessingproperties and devices in high-T
119888superconductorsrdquo Supercon-
ductor Science and Technology vol 3 no 1 1990[4] T K Worthington W J Gallagher and T R Dinger
ldquoAnisotropic nature of high-temperature superconductivity insingle-crystal Y
1Ba2Cu
3O7minus119909
rdquo Physical Review Letters vol 59no 10 pp 1160ndash1163 1987
[5] D R Harshman G Aeppli E J Ansaldo et al ldquoTemperaturedependence of the magnetic penetration depth in the high-T119888superconductor Ba
2YCu3O9minus120593
evidence for conventional s-wave pairingrdquo Physical Review B vol 36 no 4 pp 2386ndash23891987
[6] A Davidson and M Tinkham ldquoPhenomenological equationsfor the electrical conductivity of microscopically inhomoge-neousmaterialsrdquo Physical Review B vol 13 no 8 pp 3261ndash32671976
[7] J W Essam ldquoPercolation theoryrdquo Reports on Progress in Physicsvol 43 no 7 pp 833ndash912 1980
[8] M Sahimi Application of Percolation Theory Taylor amp FrancisLondon UK 1994
[9] K Osamura N Matsukura Y Kusumoto S Ochiai B Niand T Matsushita ldquoImprovement of critical current density inYBa2Cu3O6+119909
superconductor by Sn additionrdquo Japanese Journalof Applied Physics vol 29 no 9 pp L1621ndashL1623 1990
[10] S H Wee A Goyal Y L Zuev C Cantoni V Selvaman-ickam and E D Specht ldquoFormation of self-assembled double-perovskite Ba
2YNbO
6nanocolumns and their contribution to
flux-pinning and J119888in Nb-doped YBa2Cu3O7minus120575 filmsrdquo Applied
Physics Express vol 3 no 2 Article ID 023101 2010
International Journal of Superconductivity 7
[11] M Coll S Ye V Rouco et al ldquoSolution-derived YBa2Cu3O7minus120575
nanocomposite films with a Ba2YTaO
6secondary phase for
improved superconducting propertiesrdquo Superconductor Scienceand Technology vol 26 no 1 Article ID 015001 2012
[12] P P Rejith S Vidya S Vipinlal Solomon and J K ThomasldquoFlux-pinning properties of nanocrystalline HfO
2add
YBa2Cu3O7minus120575
superconductorrdquo Physica Status Solidi B vol 251pp 809ndash814 2014
[13] S A Harrington J H Durrell B Maiorov et al ldquorare earthtantalate pyrochlore nanoparticles for superior flux inYBa2Cu3119874
7minus120575filmsrdquo Superconductor Science and Technology
vol 22 no 2 Article ID 022001 2009[14] Y P Yadava E Montarroyos J M Ferreira and J Albino
Aguiar ldquoSynthesis and study of the structural characteristicsof a new complex perovskite oxide Sr
2HoHfO
55for its use
as a substrate for YBCO superconducting filmsrdquo Physica CSuperconductivity vol 354 no 1ndash4 pp 444ndash448 2001
[15] J Koshy J K Thomas J Kurian Y P Yadava and AD Damodaran ldquoDevelopment and characterization ofGdBa
2NbO6 a new ceramic substrate for YBCO thick filmsrdquo
Materials Letters vol 17 no 6 pp 393ndash397 1993[16] R Jose A M John J K Thomas et al ldquoSynthesis crystal
structure dielectric properties and potential use of nanocrys-talline complex perovskite ceramic oxide Ba
2ErZrO
55rdquoMateri-
als Research Bulletin vol 42 no 12 pp 1976ndash1985 2007[17] K V Paulose M T Sebastian K R Nair J Koshy and
A D Damodaran ldquoSynthesis of Ba2YZrO
6 a new phase in
YBa2Cu3O7-ZrO2system and its suitability as a substrate
material for YBCO filmsrdquo Solid State Communications vol 83no 12 pp 985ndash988 1992
[18] J M Phillips ldquoSubstrate selection for high-temperature super-conducting thin filmsrdquo Journal of Applied Physics vol 79 no 4pp 1829ndash1848 1996
[19] S Vidya K CMathai P P Rejith S Solomon and J KThomasldquoSmBa
2NbO6nanopowders an effective percolation network
medium for YBCO superconductorsrdquo Advances in MaterialsScience and Engineering vol 2013 Article ID 578434 7 pages2013
[20] J Kurian P R S Wariar P K Sajith and J Koshy ldquoPercolationbehavior of the normal-state resistivity and superconductivityof the YBa
2Cu3O7minus120575
-Ba2GdNbO
6composite systemrdquo Journal of
Superconductivity and Novel Magnetism vol 11 no 6 pp 683ndash687 1998
[21] P R S Wariar J Koshy J Kurian Y P Yadava and A DDamodaran ldquoPercolation studies in SmBa
2SbO6-YBa2Cu3O7minus120575
composite systemrdquo Modern Physics Letters B vol 9 no 10 p585 1995
[22] H Tovar O O Dıaz D A L Tellez and J Roa-RojasldquoBa2NdZrO
55as a potential substrate material for
YBa2Cu3O7minus120575
superconducting filmsrdquo Physica Status SolidiC Current Topics in Solid State Physics vol 4 no 11 pp4294ndash4297 2007
[23] O O Diaz L D Lopez Carreno J Albino Aguiar J Roa-Rojasand D A Landınez Tellez ldquotructural ordering chemical sta-bility and percolative effect analysis in YSr
2SbO6YBa2Cu3O7minus120575
complex perovskite compositesrdquo Physica C vol 408ndash410 pp886ndash888 2004
[24] Q Madueno D A Landınez Tellez and J Roa-Rojas ldquoProduc-tion and characterization of Ba
2NdSbO
6complex perovskite as
a substrate for YBa2Cu3O7minus120575
superconducting filmsrdquo ModernPhysics Letters B vol 20 p 427 2006
[25] K V Paulose M K Jayaraj J Koshy and A D DamodaranldquoPreparation and properties of Ba
2YZrO
6YBa2Cu3O7compos-
itesrdquo Solid State Communications vol 87 no 2 pp 147ndash1501993
[26] R Jose J James A M John D Sundararaman R Divakar andJ Koshy ldquoNew combustion process for nanosized YBa
2ZrO55
powdersrdquo Nanostructured Materials vol 11 no 5 pp 623ndash6291999
[27] J J Lin W Y Lin and R F Tsui ldquoElectrical transport andsuperconductivity in the Al
2O3-Bi2Sr18Ca12Cu2Oy and MgO-
Bi2Sr18Ca12Cu2O119910compositesrdquo Physica C vol 210 no 3-4 pp
455ndash462 1993[28] M Eisterer J Emhofer S Sorta M Zehetmayer and H W
Weber ldquoConnectivity and critical currents in polycrystallineMgB2rdquo Superconductor Science and Technology vol 22 no 3
Article ID 034016 2009[29] D Stauffer and A Aharony Introduction to Percolation Theory
Taylor and Francis 1994[30] J Wu and D S McLachlan ldquoPercolation exponents and thresh-
olds obtained from the nearly ideal continuum percolationsystem graphite-boron nitriderdquo Physical Review B vol 56 no3 pp 1236ndash1248 1997
Submit your manuscripts athttpwwwhindawicom
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
High Energy PhysicsAdvances in
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
FluidsJournal of
Atomic and Molecular Physics
Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Advances in Condensed Matter Physics
OpticsInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
AstronomyAdvances in
International Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Superconductivity
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Statistical MechanicsInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
GravityJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
AstrophysicsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Physics Research International
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Solid State PhysicsJournal of
Computational Methods in Physics
Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Soft MatterJournal of
Hindawi Publishing Corporationhttpwwwhindawicom
AerodynamicsJournal of
Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
PhotonicsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Biophysics
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
ThermodynamicsJournal of
International Journal of Superconductivity 5N
orm
alise
d re
sistiv
ity (120588
120588r)
10
05
00
50 100 150 200 250 300
Temperature (K)
(a)
50 100 150 200 250 300
Temperature (K)
10
05
00
(b)
10
05
00
(c)
50 100 150 200 250 300
Temperature (K)
10
05
00
(d)
50 100 150 200 250 300
Temperature (K)
10
09
08
07
(e)
50 100 150 200 250 300
Temperature (K)
Figure 4 Temperature-normalised resistivity graph for differentvol of nano-YBZO mixed YBCO superconductor ((a) = 0 (b)= 20 (c) = 50 (d) = 70 and (e) = 80)
theory [19ndash21] However there are few others which reportedvariation from the universal values [27 30]
The values of critical current densities (119869119888) measured for
different samples at zero applied magnetic field are shownin Table 1 The self-field 119869
119888is found to be decreasing on
the addition of nanocrystalline YBZO in YBCO A judiciousexplanation is the existence of larger defect density since 119869
119888
is more sensitive to the defect density The analysis of thecurrent flow in the composite samples reveals the weak linkbehavior in the majority of grain connections But this doesnot necessarily mean that weak (Josephson) grain couplingis absent in these samples However the number of strongergrain connectionsmust be significantly above the percolationthreshold [28] which is defined as the minimum fraction fora continuous current path
YBa2Cu3O7minus120575
superconductor will start to melt anddecompose when it is sintered at higher temperature
40
35
30
25
20
15
10
0500 02 04 06 08 10
50
45
40
35
30
25
20
15
Vol of YBCO
Tem
pera
ture
coeffi
cien
t of r
esist
ivity
(120572)
log 120588
(120583Ω
m)
Figure 5 Variation of (a) normal state resistivity 120588 and (b)temperature coefficient of resistivity 120572 = (119897120588)(119889120588119889119879) at roomtemperature for different vol of YBCO
20
18
16
14
12
10
minus07 minus06 minus05 minus04 minus03 minus02 minus01
t = 168 1205880 = 508 120583Ωmlo
g 120588(120583Ω
m)
Vc = 03
log(VS minus VC)
Figure 6 Log-log plot of 120588 versus (119881119878minus 119881
119862)
40
38
36
34
32
30minus10 minus09 minus08 minus07
u = 27 1205889984000 = 5831 times 104 120583Ωm
log 120588
998400(120583Ω
m)
Vc = 03
log(VC minus VS)
Figure 7 Log-log plot of 120588 versus (119881119862minus 119881
119878)
6 International Journal of Superconductivity
Table 1 Sintering temperature density and electric transport data of different YBCO-nano-YBZO composites
Vol of YBCO Vol of YBZO Sintering temp (∘C) Density (gm cmminus3) 119879
119888(K) Self-field 119869
119888(times104 Acm2)
100 0 975 535 92 14790 10 983 557 92 08880 20 990 566 905 02670 30 1000 575 89 00950 50 1015 584 82 mdash30 70 1120 588 mdash mdash20 80 1230 603 mdash mdash10 90 1370 615 mdash mdash0 100 1500 627 mdash mdash
The values of 119881119862 119905 and 119906 obtained for different systems
of composites vary due to many factors The critical expo-nents 119905 and 119906 are a measure of the order of interactionbetween normal metal and insulator The value for idealpercolation threshold is around 17 vol of metal in thesystem for a perfect metal-insulator composite without anyinteraction or reaction between the two The normal stateand superconducting percolation threshold values of YBCO-nano-YBZO (03 vol of YBCO) composites are in closerranges as expected for an idealized percolation system and arelower than those observed in conventionally preparedYBZO-YBCO (035 vol of YBCO) composite [25] This may bedue to the better chemical nonreactivity between YBCO andnano-YBZO Furthermore there is a negligible conductivitybelow percolation threshold while it is expected to be zeroin ideal percolative systemsThe nonreactivity of YBCOwithnano-YBZO even at high processing temperature also pointsto the fact that nano-YBZO is a suitable substrate for YBCOsuperconductor and thus to develop devices based on hightemperature superconductor films and junctions
4 Conclusion
In this paper we have studied the chemical reactivityand percolation behavior using electric transport mea-surements in polycrystalline YBa
2Cu3O7minus120575
superconductor-nano-YBa
2ZrO55
composite From structural analysis it isobserved that the mixture of materials YBa
2ZrO55
insulatorwith YBa
2Cu3O7minus120575
superconductor is a system where theparticles of superconductor and insulator materials are foundto coexist in a composite with two well-defined separatephases Resistivity measurements of the composites synthe-sized in this work show an apparent percolative behavior withpercolation threshold 119881
119862= 03 and critical exponents values
119905 = 168 and 119906 = 27 Compared to the conventionally pre-pared YBZO nanocrystalline YBZO mixed superconductor-insulator system showed a better percolation behavior Thusas discussed earlier YBZO is chemically stable with theYBCO superconductor and at the same time it did not haveany deteriorating effect on the superconducting propertycharacterized by the transition temperature
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
Acknowledgment
SukumariammaVidya acknowledgesCSIR for financial assis-tance
References
[1] T van Duzer ldquoSuperconductor electronicsrdquo Cryogenics vol 30no 12 pp 980ndash995 1990
[2] T van Duzer ldquoSuperconductor electronics and power applica-tionsrdquo Proceedings of the IEEE vol 100 no 11 pp 2993ndash29952012
[3] N McN Alford T W Button and J D Birchall ldquoProcessingproperties and devices in high-T
119888superconductorsrdquo Supercon-
ductor Science and Technology vol 3 no 1 1990[4] T K Worthington W J Gallagher and T R Dinger
ldquoAnisotropic nature of high-temperature superconductivity insingle-crystal Y
1Ba2Cu
3O7minus119909
rdquo Physical Review Letters vol 59no 10 pp 1160ndash1163 1987
[5] D R Harshman G Aeppli E J Ansaldo et al ldquoTemperaturedependence of the magnetic penetration depth in the high-T119888superconductor Ba
2YCu3O9minus120593
evidence for conventional s-wave pairingrdquo Physical Review B vol 36 no 4 pp 2386ndash23891987
[6] A Davidson and M Tinkham ldquoPhenomenological equationsfor the electrical conductivity of microscopically inhomoge-neousmaterialsrdquo Physical Review B vol 13 no 8 pp 3261ndash32671976
[7] J W Essam ldquoPercolation theoryrdquo Reports on Progress in Physicsvol 43 no 7 pp 833ndash912 1980
[8] M Sahimi Application of Percolation Theory Taylor amp FrancisLondon UK 1994
[9] K Osamura N Matsukura Y Kusumoto S Ochiai B Niand T Matsushita ldquoImprovement of critical current density inYBa2Cu3O6+119909
superconductor by Sn additionrdquo Japanese Journalof Applied Physics vol 29 no 9 pp L1621ndashL1623 1990
[10] S H Wee A Goyal Y L Zuev C Cantoni V Selvaman-ickam and E D Specht ldquoFormation of self-assembled double-perovskite Ba
2YNbO
6nanocolumns and their contribution to
flux-pinning and J119888in Nb-doped YBa2Cu3O7minus120575 filmsrdquo Applied
Physics Express vol 3 no 2 Article ID 023101 2010
International Journal of Superconductivity 7
[11] M Coll S Ye V Rouco et al ldquoSolution-derived YBa2Cu3O7minus120575
nanocomposite films with a Ba2YTaO
6secondary phase for
improved superconducting propertiesrdquo Superconductor Scienceand Technology vol 26 no 1 Article ID 015001 2012
[12] P P Rejith S Vidya S Vipinlal Solomon and J K ThomasldquoFlux-pinning properties of nanocrystalline HfO
2add
YBa2Cu3O7minus120575
superconductorrdquo Physica Status Solidi B vol 251pp 809ndash814 2014
[13] S A Harrington J H Durrell B Maiorov et al ldquorare earthtantalate pyrochlore nanoparticles for superior flux inYBa2Cu3119874
7minus120575filmsrdquo Superconductor Science and Technology
vol 22 no 2 Article ID 022001 2009[14] Y P Yadava E Montarroyos J M Ferreira and J Albino
Aguiar ldquoSynthesis and study of the structural characteristicsof a new complex perovskite oxide Sr
2HoHfO
55for its use
as a substrate for YBCO superconducting filmsrdquo Physica CSuperconductivity vol 354 no 1ndash4 pp 444ndash448 2001
[15] J Koshy J K Thomas J Kurian Y P Yadava and AD Damodaran ldquoDevelopment and characterization ofGdBa
2NbO6 a new ceramic substrate for YBCO thick filmsrdquo
Materials Letters vol 17 no 6 pp 393ndash397 1993[16] R Jose A M John J K Thomas et al ldquoSynthesis crystal
structure dielectric properties and potential use of nanocrys-talline complex perovskite ceramic oxide Ba
2ErZrO
55rdquoMateri-
als Research Bulletin vol 42 no 12 pp 1976ndash1985 2007[17] K V Paulose M T Sebastian K R Nair J Koshy and
A D Damodaran ldquoSynthesis of Ba2YZrO
6 a new phase in
YBa2Cu3O7-ZrO2system and its suitability as a substrate
material for YBCO filmsrdquo Solid State Communications vol 83no 12 pp 985ndash988 1992
[18] J M Phillips ldquoSubstrate selection for high-temperature super-conducting thin filmsrdquo Journal of Applied Physics vol 79 no 4pp 1829ndash1848 1996
[19] S Vidya K CMathai P P Rejith S Solomon and J KThomasldquoSmBa
2NbO6nanopowders an effective percolation network
medium for YBCO superconductorsrdquo Advances in MaterialsScience and Engineering vol 2013 Article ID 578434 7 pages2013
[20] J Kurian P R S Wariar P K Sajith and J Koshy ldquoPercolationbehavior of the normal-state resistivity and superconductivityof the YBa
2Cu3O7minus120575
-Ba2GdNbO
6composite systemrdquo Journal of
Superconductivity and Novel Magnetism vol 11 no 6 pp 683ndash687 1998
[21] P R S Wariar J Koshy J Kurian Y P Yadava and A DDamodaran ldquoPercolation studies in SmBa
2SbO6-YBa2Cu3O7minus120575
composite systemrdquo Modern Physics Letters B vol 9 no 10 p585 1995
[22] H Tovar O O Dıaz D A L Tellez and J Roa-RojasldquoBa2NdZrO
55as a potential substrate material for
YBa2Cu3O7minus120575
superconducting filmsrdquo Physica Status SolidiC Current Topics in Solid State Physics vol 4 no 11 pp4294ndash4297 2007
[23] O O Diaz L D Lopez Carreno J Albino Aguiar J Roa-Rojasand D A Landınez Tellez ldquotructural ordering chemical sta-bility and percolative effect analysis in YSr
2SbO6YBa2Cu3O7minus120575
complex perovskite compositesrdquo Physica C vol 408ndash410 pp886ndash888 2004
[24] Q Madueno D A Landınez Tellez and J Roa-Rojas ldquoProduc-tion and characterization of Ba
2NdSbO
6complex perovskite as
a substrate for YBa2Cu3O7minus120575
superconducting filmsrdquo ModernPhysics Letters B vol 20 p 427 2006
[25] K V Paulose M K Jayaraj J Koshy and A D DamodaranldquoPreparation and properties of Ba
2YZrO
6YBa2Cu3O7compos-
itesrdquo Solid State Communications vol 87 no 2 pp 147ndash1501993
[26] R Jose J James A M John D Sundararaman R Divakar andJ Koshy ldquoNew combustion process for nanosized YBa
2ZrO55
powdersrdquo Nanostructured Materials vol 11 no 5 pp 623ndash6291999
[27] J J Lin W Y Lin and R F Tsui ldquoElectrical transport andsuperconductivity in the Al
2O3-Bi2Sr18Ca12Cu2Oy and MgO-
Bi2Sr18Ca12Cu2O119910compositesrdquo Physica C vol 210 no 3-4 pp
455ndash462 1993[28] M Eisterer J Emhofer S Sorta M Zehetmayer and H W
Weber ldquoConnectivity and critical currents in polycrystallineMgB2rdquo Superconductor Science and Technology vol 22 no 3
Article ID 034016 2009[29] D Stauffer and A Aharony Introduction to Percolation Theory
Taylor and Francis 1994[30] J Wu and D S McLachlan ldquoPercolation exponents and thresh-
olds obtained from the nearly ideal continuum percolationsystem graphite-boron nitriderdquo Physical Review B vol 56 no3 pp 1236ndash1248 1997
Submit your manuscripts athttpwwwhindawicom
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
High Energy PhysicsAdvances in
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
FluidsJournal of
Atomic and Molecular Physics
Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Advances in Condensed Matter Physics
OpticsInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
AstronomyAdvances in
International Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Superconductivity
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Statistical MechanicsInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
GravityJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
AstrophysicsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Physics Research International
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Solid State PhysicsJournal of
Computational Methods in Physics
Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Soft MatterJournal of
Hindawi Publishing Corporationhttpwwwhindawicom
AerodynamicsJournal of
Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
PhotonicsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Biophysics
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
ThermodynamicsJournal of
6 International Journal of Superconductivity
Table 1 Sintering temperature density and electric transport data of different YBCO-nano-YBZO composites
Vol of YBCO Vol of YBZO Sintering temp (∘C) Density (gm cmminus3) 119879
119888(K) Self-field 119869
119888(times104 Acm2)
100 0 975 535 92 14790 10 983 557 92 08880 20 990 566 905 02670 30 1000 575 89 00950 50 1015 584 82 mdash30 70 1120 588 mdash mdash20 80 1230 603 mdash mdash10 90 1370 615 mdash mdash0 100 1500 627 mdash mdash
The values of 119881119862 119905 and 119906 obtained for different systems
of composites vary due to many factors The critical expo-nents 119905 and 119906 are a measure of the order of interactionbetween normal metal and insulator The value for idealpercolation threshold is around 17 vol of metal in thesystem for a perfect metal-insulator composite without anyinteraction or reaction between the two The normal stateand superconducting percolation threshold values of YBCO-nano-YBZO (03 vol of YBCO) composites are in closerranges as expected for an idealized percolation system and arelower than those observed in conventionally preparedYBZO-YBCO (035 vol of YBCO) composite [25] This may bedue to the better chemical nonreactivity between YBCO andnano-YBZO Furthermore there is a negligible conductivitybelow percolation threshold while it is expected to be zeroin ideal percolative systemsThe nonreactivity of YBCOwithnano-YBZO even at high processing temperature also pointsto the fact that nano-YBZO is a suitable substrate for YBCOsuperconductor and thus to develop devices based on hightemperature superconductor films and junctions
4 Conclusion
In this paper we have studied the chemical reactivityand percolation behavior using electric transport mea-surements in polycrystalline YBa
2Cu3O7minus120575
superconductor-nano-YBa
2ZrO55
composite From structural analysis it isobserved that the mixture of materials YBa
2ZrO55
insulatorwith YBa
2Cu3O7minus120575
superconductor is a system where theparticles of superconductor and insulator materials are foundto coexist in a composite with two well-defined separatephases Resistivity measurements of the composites synthe-sized in this work show an apparent percolative behavior withpercolation threshold 119881
119862= 03 and critical exponents values
119905 = 168 and 119906 = 27 Compared to the conventionally pre-pared YBZO nanocrystalline YBZO mixed superconductor-insulator system showed a better percolation behavior Thusas discussed earlier YBZO is chemically stable with theYBCO superconductor and at the same time it did not haveany deteriorating effect on the superconducting propertycharacterized by the transition temperature
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
Acknowledgment
SukumariammaVidya acknowledgesCSIR for financial assis-tance
References
[1] T van Duzer ldquoSuperconductor electronicsrdquo Cryogenics vol 30no 12 pp 980ndash995 1990
[2] T van Duzer ldquoSuperconductor electronics and power applica-tionsrdquo Proceedings of the IEEE vol 100 no 11 pp 2993ndash29952012
[3] N McN Alford T W Button and J D Birchall ldquoProcessingproperties and devices in high-T
119888superconductorsrdquo Supercon-
ductor Science and Technology vol 3 no 1 1990[4] T K Worthington W J Gallagher and T R Dinger
ldquoAnisotropic nature of high-temperature superconductivity insingle-crystal Y
1Ba2Cu
3O7minus119909
rdquo Physical Review Letters vol 59no 10 pp 1160ndash1163 1987
[5] D R Harshman G Aeppli E J Ansaldo et al ldquoTemperaturedependence of the magnetic penetration depth in the high-T119888superconductor Ba
2YCu3O9minus120593
evidence for conventional s-wave pairingrdquo Physical Review B vol 36 no 4 pp 2386ndash23891987
[6] A Davidson and M Tinkham ldquoPhenomenological equationsfor the electrical conductivity of microscopically inhomoge-neousmaterialsrdquo Physical Review B vol 13 no 8 pp 3261ndash32671976
[7] J W Essam ldquoPercolation theoryrdquo Reports on Progress in Physicsvol 43 no 7 pp 833ndash912 1980
[8] M Sahimi Application of Percolation Theory Taylor amp FrancisLondon UK 1994
[9] K Osamura N Matsukura Y Kusumoto S Ochiai B Niand T Matsushita ldquoImprovement of critical current density inYBa2Cu3O6+119909
superconductor by Sn additionrdquo Japanese Journalof Applied Physics vol 29 no 9 pp L1621ndashL1623 1990
[10] S H Wee A Goyal Y L Zuev C Cantoni V Selvaman-ickam and E D Specht ldquoFormation of self-assembled double-perovskite Ba
2YNbO
6nanocolumns and their contribution to
flux-pinning and J119888in Nb-doped YBa2Cu3O7minus120575 filmsrdquo Applied
Physics Express vol 3 no 2 Article ID 023101 2010
International Journal of Superconductivity 7
[11] M Coll S Ye V Rouco et al ldquoSolution-derived YBa2Cu3O7minus120575
nanocomposite films with a Ba2YTaO
6secondary phase for
improved superconducting propertiesrdquo Superconductor Scienceand Technology vol 26 no 1 Article ID 015001 2012
[12] P P Rejith S Vidya S Vipinlal Solomon and J K ThomasldquoFlux-pinning properties of nanocrystalline HfO
2add
YBa2Cu3O7minus120575
superconductorrdquo Physica Status Solidi B vol 251pp 809ndash814 2014
[13] S A Harrington J H Durrell B Maiorov et al ldquorare earthtantalate pyrochlore nanoparticles for superior flux inYBa2Cu3119874
7minus120575filmsrdquo Superconductor Science and Technology
vol 22 no 2 Article ID 022001 2009[14] Y P Yadava E Montarroyos J M Ferreira and J Albino
Aguiar ldquoSynthesis and study of the structural characteristicsof a new complex perovskite oxide Sr
2HoHfO
55for its use
as a substrate for YBCO superconducting filmsrdquo Physica CSuperconductivity vol 354 no 1ndash4 pp 444ndash448 2001
[15] J Koshy J K Thomas J Kurian Y P Yadava and AD Damodaran ldquoDevelopment and characterization ofGdBa
2NbO6 a new ceramic substrate for YBCO thick filmsrdquo
Materials Letters vol 17 no 6 pp 393ndash397 1993[16] R Jose A M John J K Thomas et al ldquoSynthesis crystal
structure dielectric properties and potential use of nanocrys-talline complex perovskite ceramic oxide Ba
2ErZrO
55rdquoMateri-
als Research Bulletin vol 42 no 12 pp 1976ndash1985 2007[17] K V Paulose M T Sebastian K R Nair J Koshy and
A D Damodaran ldquoSynthesis of Ba2YZrO
6 a new phase in
YBa2Cu3O7-ZrO2system and its suitability as a substrate
material for YBCO filmsrdquo Solid State Communications vol 83no 12 pp 985ndash988 1992
[18] J M Phillips ldquoSubstrate selection for high-temperature super-conducting thin filmsrdquo Journal of Applied Physics vol 79 no 4pp 1829ndash1848 1996
[19] S Vidya K CMathai P P Rejith S Solomon and J KThomasldquoSmBa
2NbO6nanopowders an effective percolation network
medium for YBCO superconductorsrdquo Advances in MaterialsScience and Engineering vol 2013 Article ID 578434 7 pages2013
[20] J Kurian P R S Wariar P K Sajith and J Koshy ldquoPercolationbehavior of the normal-state resistivity and superconductivityof the YBa
2Cu3O7minus120575
-Ba2GdNbO
6composite systemrdquo Journal of
Superconductivity and Novel Magnetism vol 11 no 6 pp 683ndash687 1998
[21] P R S Wariar J Koshy J Kurian Y P Yadava and A DDamodaran ldquoPercolation studies in SmBa
2SbO6-YBa2Cu3O7minus120575
composite systemrdquo Modern Physics Letters B vol 9 no 10 p585 1995
[22] H Tovar O O Dıaz D A L Tellez and J Roa-RojasldquoBa2NdZrO
55as a potential substrate material for
YBa2Cu3O7minus120575
superconducting filmsrdquo Physica Status SolidiC Current Topics in Solid State Physics vol 4 no 11 pp4294ndash4297 2007
[23] O O Diaz L D Lopez Carreno J Albino Aguiar J Roa-Rojasand D A Landınez Tellez ldquotructural ordering chemical sta-bility and percolative effect analysis in YSr
2SbO6YBa2Cu3O7minus120575
complex perovskite compositesrdquo Physica C vol 408ndash410 pp886ndash888 2004
[24] Q Madueno D A Landınez Tellez and J Roa-Rojas ldquoProduc-tion and characterization of Ba
2NdSbO
6complex perovskite as
a substrate for YBa2Cu3O7minus120575
superconducting filmsrdquo ModernPhysics Letters B vol 20 p 427 2006
[25] K V Paulose M K Jayaraj J Koshy and A D DamodaranldquoPreparation and properties of Ba
2YZrO
6YBa2Cu3O7compos-
itesrdquo Solid State Communications vol 87 no 2 pp 147ndash1501993
[26] R Jose J James A M John D Sundararaman R Divakar andJ Koshy ldquoNew combustion process for nanosized YBa
2ZrO55
powdersrdquo Nanostructured Materials vol 11 no 5 pp 623ndash6291999
[27] J J Lin W Y Lin and R F Tsui ldquoElectrical transport andsuperconductivity in the Al
2O3-Bi2Sr18Ca12Cu2Oy and MgO-
Bi2Sr18Ca12Cu2O119910compositesrdquo Physica C vol 210 no 3-4 pp
455ndash462 1993[28] M Eisterer J Emhofer S Sorta M Zehetmayer and H W
Weber ldquoConnectivity and critical currents in polycrystallineMgB2rdquo Superconductor Science and Technology vol 22 no 3
Article ID 034016 2009[29] D Stauffer and A Aharony Introduction to Percolation Theory
Taylor and Francis 1994[30] J Wu and D S McLachlan ldquoPercolation exponents and thresh-
olds obtained from the nearly ideal continuum percolationsystem graphite-boron nitriderdquo Physical Review B vol 56 no3 pp 1236ndash1248 1997
Submit your manuscripts athttpwwwhindawicom
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
High Energy PhysicsAdvances in
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
FluidsJournal of
Atomic and Molecular Physics
Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Advances in Condensed Matter Physics
OpticsInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
AstronomyAdvances in
International Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Superconductivity
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Statistical MechanicsInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
GravityJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
AstrophysicsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Physics Research International
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Solid State PhysicsJournal of
Computational Methods in Physics
Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Soft MatterJournal of
Hindawi Publishing Corporationhttpwwwhindawicom
AerodynamicsJournal of
Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
PhotonicsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Biophysics
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
ThermodynamicsJournal of
International Journal of Superconductivity 7
[11] M Coll S Ye V Rouco et al ldquoSolution-derived YBa2Cu3O7minus120575
nanocomposite films with a Ba2YTaO
6secondary phase for
improved superconducting propertiesrdquo Superconductor Scienceand Technology vol 26 no 1 Article ID 015001 2012
[12] P P Rejith S Vidya S Vipinlal Solomon and J K ThomasldquoFlux-pinning properties of nanocrystalline HfO
2add
YBa2Cu3O7minus120575
superconductorrdquo Physica Status Solidi B vol 251pp 809ndash814 2014
[13] S A Harrington J H Durrell B Maiorov et al ldquorare earthtantalate pyrochlore nanoparticles for superior flux inYBa2Cu3119874
7minus120575filmsrdquo Superconductor Science and Technology
vol 22 no 2 Article ID 022001 2009[14] Y P Yadava E Montarroyos J M Ferreira and J Albino
Aguiar ldquoSynthesis and study of the structural characteristicsof a new complex perovskite oxide Sr
2HoHfO
55for its use
as a substrate for YBCO superconducting filmsrdquo Physica CSuperconductivity vol 354 no 1ndash4 pp 444ndash448 2001
[15] J Koshy J K Thomas J Kurian Y P Yadava and AD Damodaran ldquoDevelopment and characterization ofGdBa
2NbO6 a new ceramic substrate for YBCO thick filmsrdquo
Materials Letters vol 17 no 6 pp 393ndash397 1993[16] R Jose A M John J K Thomas et al ldquoSynthesis crystal
structure dielectric properties and potential use of nanocrys-talline complex perovskite ceramic oxide Ba
2ErZrO
55rdquoMateri-
als Research Bulletin vol 42 no 12 pp 1976ndash1985 2007[17] K V Paulose M T Sebastian K R Nair J Koshy and
A D Damodaran ldquoSynthesis of Ba2YZrO
6 a new phase in
YBa2Cu3O7-ZrO2system and its suitability as a substrate
material for YBCO filmsrdquo Solid State Communications vol 83no 12 pp 985ndash988 1992
[18] J M Phillips ldquoSubstrate selection for high-temperature super-conducting thin filmsrdquo Journal of Applied Physics vol 79 no 4pp 1829ndash1848 1996
[19] S Vidya K CMathai P P Rejith S Solomon and J KThomasldquoSmBa
2NbO6nanopowders an effective percolation network
medium for YBCO superconductorsrdquo Advances in MaterialsScience and Engineering vol 2013 Article ID 578434 7 pages2013
[20] J Kurian P R S Wariar P K Sajith and J Koshy ldquoPercolationbehavior of the normal-state resistivity and superconductivityof the YBa
2Cu3O7minus120575
-Ba2GdNbO
6composite systemrdquo Journal of
Superconductivity and Novel Magnetism vol 11 no 6 pp 683ndash687 1998
[21] P R S Wariar J Koshy J Kurian Y P Yadava and A DDamodaran ldquoPercolation studies in SmBa
2SbO6-YBa2Cu3O7minus120575
composite systemrdquo Modern Physics Letters B vol 9 no 10 p585 1995
[22] H Tovar O O Dıaz D A L Tellez and J Roa-RojasldquoBa2NdZrO
55as a potential substrate material for
YBa2Cu3O7minus120575
superconducting filmsrdquo Physica Status SolidiC Current Topics in Solid State Physics vol 4 no 11 pp4294ndash4297 2007
[23] O O Diaz L D Lopez Carreno J Albino Aguiar J Roa-Rojasand D A Landınez Tellez ldquotructural ordering chemical sta-bility and percolative effect analysis in YSr
2SbO6YBa2Cu3O7minus120575
complex perovskite compositesrdquo Physica C vol 408ndash410 pp886ndash888 2004
[24] Q Madueno D A Landınez Tellez and J Roa-Rojas ldquoProduc-tion and characterization of Ba
2NdSbO
6complex perovskite as
a substrate for YBa2Cu3O7minus120575
superconducting filmsrdquo ModernPhysics Letters B vol 20 p 427 2006
[25] K V Paulose M K Jayaraj J Koshy and A D DamodaranldquoPreparation and properties of Ba
2YZrO
6YBa2Cu3O7compos-
itesrdquo Solid State Communications vol 87 no 2 pp 147ndash1501993
[26] R Jose J James A M John D Sundararaman R Divakar andJ Koshy ldquoNew combustion process for nanosized YBa
2ZrO55
powdersrdquo Nanostructured Materials vol 11 no 5 pp 623ndash6291999
[27] J J Lin W Y Lin and R F Tsui ldquoElectrical transport andsuperconductivity in the Al
2O3-Bi2Sr18Ca12Cu2Oy and MgO-
Bi2Sr18Ca12Cu2O119910compositesrdquo Physica C vol 210 no 3-4 pp
455ndash462 1993[28] M Eisterer J Emhofer S Sorta M Zehetmayer and H W
Weber ldquoConnectivity and critical currents in polycrystallineMgB2rdquo Superconductor Science and Technology vol 22 no 3
Article ID 034016 2009[29] D Stauffer and A Aharony Introduction to Percolation Theory
Taylor and Francis 1994[30] J Wu and D S McLachlan ldquoPercolation exponents and thresh-
olds obtained from the nearly ideal continuum percolationsystem graphite-boron nitriderdquo Physical Review B vol 56 no3 pp 1236ndash1248 1997
Submit your manuscripts athttpwwwhindawicom
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
High Energy PhysicsAdvances in
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
FluidsJournal of
Atomic and Molecular Physics
Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Advances in Condensed Matter Physics
OpticsInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
AstronomyAdvances in
International Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Superconductivity
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Statistical MechanicsInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
GravityJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
AstrophysicsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Physics Research International
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Solid State PhysicsJournal of
Computational Methods in Physics
Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Soft MatterJournal of
Hindawi Publishing Corporationhttpwwwhindawicom
AerodynamicsJournal of
Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
PhotonicsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Biophysics
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
ThermodynamicsJournal of
Submit your manuscripts athttpwwwhindawicom
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
High Energy PhysicsAdvances in
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
FluidsJournal of
Atomic and Molecular Physics
Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Advances in Condensed Matter Physics
OpticsInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
AstronomyAdvances in
International Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Superconductivity
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Statistical MechanicsInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
GravityJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
AstrophysicsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Physics Research International
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Solid State PhysicsJournal of
Computational Methods in Physics
Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Soft MatterJournal of
Hindawi Publishing Corporationhttpwwwhindawicom
AerodynamicsJournal of
Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
PhotonicsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Biophysics
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
ThermodynamicsJournal of