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Coated Conductors for Applications (CCA) 2016, Aspen, Colorado, USA, September 11-14, 2016

Temperature Dependence of Critical Currents in REBCO Coated Conductors

with Artificial Pinning Centers

K. Matsumoto, M. Nishihara, T. Horide, A. K. JhaKyushu Institute of Technology

A. Ichinose, Y. Yoshida, S. Awaji, CRIEPI, Nagoya University, Tohoku Univ.

✓ Critical Current✓ Anisotropy✓ Grain Boundary✓ Homogeneity✓ AC loss✓ Mechanical property✓ Stability✓ Mass production✓ Costhttp://www.fujikura.co.jp/f‐news/1191427_4018.html

http://www.magnet.fsu.edu/mediacenter/publications/

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Issues in Coated Conductor R & D

✓ Critical Current✓ Anisotropy✓ Grain Boundary✓ Homogeneity✓ AC loss✓ Mechanical property✓ Stability✓ Mass production✓ Cost

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Artificial pinning centers “APCs” －Nanorods

Nanorods

BaZrO3, BaSnO3, Double perovskite, BaHfO3 ,etc

J. MacManus‐Driscoll et al., Nature Mat. 3, 439 (2004) 

BaZrO3 column

D. Feldmann et al., SUST 23, 095004 (2010) 

Ba2YNbO6 nanorods

Fpmax = 32.3 GN/m3 at 75 K, B//c

H. Tobita et al., SUST 25, 062002 (2012) J. Hanisch et al., SUST 19, 534 (2006) 

BaHfO3 nanorods

A. Tsuruta et al., SUST 27, 065001 (2014) 

Fpmax = 28.0 GN/m3 at 77.K, B//c

P. Mele et al., SUST 21, 032002 (2008) 

BaSnO3 nanorods

Fpmax = 28.3 GN/m3 at 77 K, B//c

C. Varanasi et al., APL 93, 092501 (2008) 

✓ Selection of material and

✓ Straightness of nanorods✓ Appropriate diameter of nanorods

✓ Sharp interface

✓ High density without Tc suppression

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Nanoparticles

Artificial pinning centers －Nanoparticles

Y211, Y2O3, BaZrO3, BaSnO3, etc

T. Haugan et al., Nature 430, 867 (2004)

Y211 particles

P. Mele et al., SUST 20, 616 (2007)

Y2O3 particles

Fpmax = 16 GN/m3 at 77 K, B//c

J. Gutierrez et al., Nature Mat. 6, 367 (2007)

BaZrO3 particles

Fpmax = 21 GN/m3 at 77 K, B//c

A. Llordes et al., Nature Mat. 11, 329 (2012)

BaZrO3 particles

Nanoscale strain

M. Miura et al., SUST 26, 035008 (2013)

BaZrO3BaSnO3BaNbO3pure

✓ Selection of material and

✓ Appropriate diameter of nanoparticles

✓ High density without Tc suppression

✓ Sharp interface

✓ Surrounding additional defects

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Variation in APC structures-Hybrid, MLs, segmentation

A. Kiessling et al., SUST 24, 055018  (2011) 

MLs

G. Ercolano et al., SUST 24, 095012  (2011) 

(Nb‐Ta)YBCO

Fpmax = 26 GN/m3 at 77 K, B//cB. Maiorov et al., Nature Mat. 8, 398 (2009)

Segmentation

T. Horide et al., APL 92, 182511 (2008) 

MLs + Segmentation

P. Mele et al., SUST 21, 015019 (2008) 

BaZrO3 nanorods Y2O3 particlesBaZrO3 + Y2O3Hybrid APCs

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Formation mechanism and elastic strain studies

J. Slutsker et al., PRB 73, 184127 (2006) 

Phase field model

J. MacManus‐Driscoll et al., Nature Mat. 7, 314 (2008) 

Epitaxial strain control

J. Wu et al., SUST 27, 044010 (2014) 

Modeling of nanorod strain

T. Horide et al., JJAP 53, 083101 (2014) 

FEM & first princiiple calcualation

C. Cantoni et al., ACS Nano 5, 4783 (2011) 

Strain and oxygen deficiency

A. Llordes et al., Nature Mat. 11, 329 (2012)

Strain evaluation by TEM

S. Wee  et al., Adv. Func. Mat. 23, 1912 (2013) 

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What should we do next?Nanoscience of flux pinning for coated conductorshas been developing extensively

Development of appropriate pinning centers intocoated conductors for tuning of flux pinningunder the desired temperature and the magneticfield

Appropriate tuning of Jc anisotropy for coildesign

Development of appropriate pinning centers forimprovement of Je

Understanding of flux pinning mechanism ofcoated conductors is very important !

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Recent results of flux pinning R&D

T. Horide et al., APL 108, 082601 (2016)S. Miura et al., APL Mter. 4, 016102 (2016)

Matching field is a key point

> 60 MA/cm2

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Saturation problem of Fp-B curve by nanorod APC

S. Awaji et al., J. Appl. Phys. 111, 013914 (2012)

Fprand :Random pinning force density

Fpcorr :Correlated pinning force density

Fp Fpcorr : B < B

Fp Fprand 2

Fpcorr 2 : B > B

Direct summation, B<BΦ Partial plastic flow, B>BΦ

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Comparison between measured Jc and theoretical limit Jd

02

03 3dJ

λ(T)= λ(0)(1-T/Tc)-1/2

ξ(T)= ξ(0)(1-T/Tc)-1/2

λ(0)=150 nm, ξ(0)=1.5 nm

Jd(4.2 K, 0 T) = 280 MA/cm2

Jd(77 K, 0 T) = 43 MA/cm2

Jc(4.2 K, 0 T) = 60 MA/cm2, Jc/Jd = 21 %Jc(77 K, 0 T) = 8 MA/cm2, Jc/Jd = 18 %

* NbTi wire, Jc/Jd = 5‒10 %

There is still room for the improvement!

B (T) B (T)F

pJ c

Theoretical limit

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Fabrication of BHO nanorods doped GdBCO films

GdBCOBHO

Growth temperature 780ºC

Distance 70 mm

Frequency 1‒10 Hz

pO2 400 mTorr

Substrate LaAlO3 (100)

Pulse number 6000

Energy density 1.5 J/cm2

0vol% 4 vol% 5 vol% 6 vol% 10 vol%

Sample pure 25:1 20:1 39:2 78:4 15:1 20:2 39:4 78:8

GdBCO (pulse) 6000 5770 5714 5707 5707 5625 5456 5442 5442

BHO (pulse) 0 230 286 293 293 375 545 558 558

Thickness (nm) 254 243 150 178 238 243 150 141 165

Alternating target method GdBa2Cu3O7‐x BaHfO3

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Birr curves for BHO doped GdBCO films

T (K)

B irr(T)

20:1

78:4

78:8

39:4

B//c

K. Matsumoto et al., J. Appl. Phys. 116, 163903 (2014)

BΦ≈ 4 TBΦ≈ 5 T

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Jc-B of BHO doped GdBCO films at 65 - 77 K

J c(M

A/cm

2 )θ (deg.)

65 K, 4 T

20:1

25:1

77 K, 2 T

20:1

25:1

pure15:1

pure

15:1

B (T)

J c(M

A/cm

2 )

B//c

20:1

25:1pure15:1

20:1

25:1

pure15:1

65 K

77 K

20:1 shows the highest Jc at 65 & 77 K Jc peak appeared at B//c for 20:1 specimen

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Jc and Fp of BHO doped GdBCO at 10 - 40 K

B (T)

F p(GN/m

3 )

20:1, 10K

25:1, 10K39:2, 10K

pure, 10K

20:1, 20K

25:1, 20K

39:2, 20K

pure, 20K

20:1, 40K

25:1, 40K

39:2, 40Kpure, 40K

B//c

B (T)

J c(M

A/cm

2 )

20:1, 10K

25:1, 10K

39:2, 10K

pure, 10K

20:1, 20K

25:1, 20K

39:2, 20K

pure, 20K

20:1, 40K

25:1, 40K

39:2, 40K

pure, 40K

B//c20

30

2

3

5

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Jc and Fp of 20:1 is the highest at 10-40 K 1 TN/m3 was observed at 10 K, and more higher value is expected at 4.2 K

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Optimization of ratio of BHO particles to GdBCO

BHO vol. %

F p(GN/m

3 )

F p(GN/m

3 )

F p(GN/m

3 )

BHO vol. %BHO vol. %

B//c, 77 K B//c, 40 K B//c, 10 K

2 T

4 T

6 T

9 T

6 T

3 T

9 T

6 T

Optimized volume fraction of BHO dopant is 5 vol.% within the whole temperature range of 10‒77 K

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Temperature dependence of Jc of BHO-GdBCO

δl pinning : n=5/2δTc pinning : n=7/6

2( ) 1 ( / )n

c cJ T T T Most of specimens show n=2.42‒3.08, ineither cases of B<BΦ and B>BΦ

In both cases, δl pinning is dominantwithin the temperature range of 20-77 K

The range of T<20 K is under studyN. Haberkorn et al., PRB 85, 014522 (2012)

m = 2.5

m = 1.2

Present, 3T

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Comparison with other group’s data

Maiorov, 0.3T

B. Maioriv et al., nature mater.  8, 398 (2009)

BZO nanorods

Yamasaki, 1T

H. Yamazaki, SUST 29, 065005 (2016) 

Y2O3 nanoparticles

MOD BZO

M. Miura, PRB 83, 184519 (2011) 

n = 1.24

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How the pinning works in BHO-GdBCO films?

B. Maioriv et al., nature mater.  8, 398 (2009)Tilted Straight

A. Tsuruta et al. : IEEE. Trans. Appl. Supercond. 23, 8001104 (2013) 

20 K<T < 60 KKink excitationRandom pins become strongSF, Intrinsic pinning, VacancyDislocation, Twin

60 K<T < 77 K kKink excitationThermal fluctuationRandom pins are weak

0 K < T < 20 KSmall kink excitationRandom pins become strongSF, Intrinsic pinning, VacancyDislocation, Twin

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H/Hc2 = 0.2,  = 15°γ= 7, T = 0

Nanorods = 10 % vol.d = 3

Nanoparticles = 2% vol.sd = 3

Can TDGL simulation tell us the better pinning?

= 15°

Magnetic field

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Current

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Jc() of REBCO films with nanorods and hybrid APCs

Jc anisotropy can be tuned by hybrid APC approach

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SummaryWe fabricated BHO doped GdBCO films toinvestigate the temperature dependence of criticalcurrent and flux pinning properties

Matching field BΦ of the specimens are 4‒5 T The GdBCO film of 20:1 ratio (5 vol.%

BHO) has the highest Jc-B characteristicsand Fp = 1 TN/m3 at 10 K

Optimized volume fraction of BHO dopant is5 vol.% within the whole temperature rangeof 10‒77 K

Temperature dependence of BHO dopedGdBCO films show δl pinning behavior