Growth and characterization of α-nickel sulphate ... · Growth and characterization of a-nickel sulphate hexahydrate single crystal P. Kathiravan a, T. Balakrishnan a,*, C. Srinath

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Karbala International Journal of Modern Science xx (2016) 1e13http://www.journals.elsevier.com/karbala-international-journal-of-modern-science/

Growth and characterization of a-nickel sulphate hexahydratesingle crystal

P. Kathiravan a, T. Balakrishnan a,*, C. Srinath b, K. Ramamurthi c, S. Thamotharan b

a Crystal Growth Laboratory, PG & Research Department of Physics, Periyar EVR College (Autonomous), Tiruchirappalli, 620023, Tamil Nadu,

Indiab Biomolecular Crystallography Laboratory, School of Chemical and Biotechnology, SASTRA University, Thanjavur, 613 401, Tamil Nadu, Indiac Department of Physics & Nano Technology, Crystal Growth and Thin Film Laboratory, Faculty of Engineering and Technology, SRM University,

Kattankulathur, 603 203, Tamil Nadu, India

Received 29 February 2016; revised 26 August 2016; accepted 26 August 2016

Abstract

Single crystal of a-nickel sulphate hexahydrate, a-NiSO4. 6H2O (a-NSH) is grown from aqueous solution by slow evaporationmethod. Solubility and metastable zone width of a-NSH are determined from the aqueous solution. The three dimensional structureis elucidated by single crystal X-ray diffraction studies. The a-NSH crystallizes in the non e centrosymmetric tetragonal spacegroup P41212. The relative contributions of various intermolecular interactions involved in the crystal structure are quantified usingHirshfeld surface analysis and the decomposed two dimensional fingerprint plots. Fourier transform infrared spectral analysis andVickers microhardness studies are carried out to characterize the grown crystal. Further the grown crystals are characterized usingTGA, DSC, UVeViseNIR and dielectric analysis. The third order nonlinear optical properties are studied by Zescan techniquewith HeeNe laser radiation of wavelength 632.8 nm and the corresponding nonlinear refractive index, absorption coefficient andoptical susceptibility are calculated. Crystalline perfection is assessed by etching studies and laser damage threshold is observed forthe grown crystal.© 2016 The Authors. Production and hosting by Elsevier B.V. on behalf of University of Kerbala. This is an open access articleunder the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Keywords: Crystal growth; X e ray diffraction; Hardness measurement; Thermal analysis; Z e scan studies

1. Introduction

Most of the crystals show continuous optical trans-mission in the wavelength ranging from ultraviolet (UV)to near infrared (NIR) but only a few crystals exhibitdiscontinuous transmittance. One of the well-known

* Corresponding author. Department of Physics, Periyar EVR

College, Tiruchirappalli 23, Tamilnadu, India.

E-mail address: [email protected] (T. Balakrishnan).

Peer review under responsibility of University of Kerbala.

http://dx.doi.org/10.1016/j.kijoms.2016.08.002

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Please cite this article in press as: P. Kathiravan et al., Growth and chara

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crystals belonging to this category is the nickel sul-phate hexahydrate, (a-NiSO4.6H2O; a-NSH). The a-NSH crystal exhibits high transmittance over a narrowrange of 250e340 nm, moderate transmittance in450e600 nm range and transmittance in the850e900 nm range and a strong absorption in otherwavelengths range; thus it behaves as an ultraviolet lightfilter and the filters of this type are also commerciallyavailable [1,2]. There are a variety of devices which usethe ultraviolet light filters to allow only selectivewavelengths of UV light to pass through. Such filters are

n behalf of University of Kerbala. This is an open access article under

4.0/).

cterization of a-nickel sulphate hexahydrate single crystal, Karbala

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Fig. 1. Solubility and nucleation curve of a-NSH.

2 P. Kathiravan et al. / Karbala International Journal of Modern Science xx (2016) 1e13

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used in missile approach warning systems, thus has theability to identify the incomingmissile [3]. The benefit ofsuch a system is its ability to estimate missile range.Further the success and efficiency of thewarning systemsfor helicopters or transport-type aircrafts depends uponsuch UV sensors [4]. Commercially available nickelsulphate hexahydrate crystals arewidely used as sensors.Several other crystals exhibiting the band-pass filterproperties are the potassium cobalt nickel sulphatehexahydrate (KCNSH) [1], cesium nickel sulphatehexahydrate (CNSH) [5], iron nickel sulphate twelvehydrate (FNSH) [6], rubidium nickel sulphate hexahy-drate (RNSH) [7] and ammonium cobalt nickel sulphatehexahydrate (ACNSH) [8]. Among these materials a-NSH is especially developed for the purpose of UV filterconstruction. a-NSH exhibits circular dichroic [9] andoptical rotation [10] in the visible regionwhichmake thiscrystal to find application as transmission - band filters.

NSH crystallizes in two polymorphs, namely a-NSHand beNSH. a-NSH is formed by spontaneous nucle-ation from aqueous solution at room temperature [11].Bright green beNSH crystallizes in monoclinic systemwith the space group C2/c [12]. Blue green coloured a-NSH crystal belongs to the tetragonal system with thespace group of P41212 and the unit-cell parameters area ¼ b ¼ 6.7837 (1) Å and c ¼ 18.2772 (6) Å [10]. Thecrystal structure of a-NSH was reported by two groups[13]. Manomenenova et al. [11], reported the rapidgrowth ofa-NSH crystals. YoupinHe et al. [14], reportedthe growth of a-NSH crystal and its application as ul-traviolet filter. Hemmati and Rezagholipour Dizaji [15]reported the unidirectional growth of a-NiSO4.6H2Ocrystal employing Sankaranarayanan and Ramasamymethod. Recently Silambarasan et al. [16] have reportedthe growth of guanidine carbonate doped nickel sulphatehexahydrate single crystal and its possible application asband-pass filters. In the present work, crystal structure ofa-NSH has been redetermined with higher precision [R-factor: 1.70%] than the previous report [R-factor:2.54%]. Hirshfeld surface is used to analyse the inter-molecular contacts present in the crystal structure.Further detailed studies on the optical, thermal, me-chanical, dielectric, chemical etching study, third ordernonlinear optical property and laser damage thresholdare carried out and results are presented in this work.

2. Experimental procedure

2.1. Solubility and nucleation curve

The solubility of a-NSH was measured using dou-ble distilled water at five different temperatures viz. 30,



35, 40, 45 and 50 �C. The solubility data was deter-mined by dissolving the synthesized salt of a-NSH in100 mL of double distilled water at a constant tem-perature with continuous stirring. After attaining thesaturation, the equilibrium concentration of the solutewas analysed gravimetrically. The same procedure wasrepeated to estimate the solubility at all the tempera-tures. Presently determined solubility data are utilizedfor the determination of metastable zone width [17].Metastable zone width of the a-NSH was estimated byconventional polythermal method [18]. In polythermalmethod the equilibrium saturated solution was cooledfrom the overheated temperature to the temperature atwhich the first speck of the solid particle is observed.Since the time taken for the formation of the firstvisible crystal after attainment of critical nucleus isvery small the first crystal observed may be taken asthe critical nucleus. The solubility curve along withnucleation curve for a-NSH is shown in Fig. 1.

2.2. Crystal growth

Single crystals of a-NSH were grown by slowevaporation solution growth technique from aqueoussolution. AR grade nickel sulphate hexahydrate wasdissolved in double distilled water and thoroughlymixed for 4 h using a magnetic stirrer and then filteredusing Whatman filter paper. The beaker containingsolution was closed with a perforated polythene sheetand kept in a dust free atmosphere for slow evaporationat room temperature. Optical quality bulk single crys-tals of 10 � 9 � 4 mm3 size were harvested in a periodof 11 days. As grown single crystals of a-nickel sul-phate hexahydrate are shown in Fig. 2.


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Fig. 2. As grown a-NSH single crystals.

Table 1

Crystal data and structure refinement of the title compound.

Empirical formula H12 Ni O10 S

Formula weight 262.87 g/mol

Temperature 293 (2) K

Wavelength 0.71073 ÅCrystal system, space group Tetragonal, P41212

Unit cell dimensions a ¼ 6.7837 (1) Å a ¼ 90 deg.

b ¼ 6.7837 (1)Å b ¼ 90 deg.

c ¼ 18.2772 (6) Å g ¼ 90 deg.

Volume 841.09 (3) Å3

Z, Calculated density 4, 2.076 Mg/m3

Absorption coefficient 2.584 mm�1

F (000) 544

Crystal size 0.30 � 0.25 � 0.20 mm3

Theta range for data collection 3.20e28.28 deg.

Limiting indices �9 � h<¼8, �8 � k<¼8,

�22 � l<¼24

Reflections collected/unique 10156/1044 [R (int) ¼ 0.0434]

Completeness to theta ¼ 28.28 100%

Absorption correction Semi-empirical from equivalents

Max. and min. Transmission 0.6260 and 0.5111

Refinement method Full-matrix least-squares on F2

Data/restraints/parameters 1044/6/81

Goodness-of-fit on F̂2 1.054

Final R indices [I>2s(I)] R1 ¼ 0.0170, wR2 ¼ 0.0373

R indices (all data) R1 ¼ 0.0201, wR2 ¼ 0.0384

Absolute structure parameter 0.003 (9)

Extinction coefficient 0.0174 (10)

Largest diff. peak and hole 0.269 and �0.235 e.Å�3

3P. Kathiravan et al. / Karbala International Journal of Modern Science xx (2016) 1e13

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2.3. Characterization studies

One of the suitable crystals was selected for thesingle crystal X-ray diffraction studies to elucidatecrystal structure using Bruker AXS Kappa apex2 CCDdiffractometer with Mo Ka radiation (l ¼ 0.71073 Å)at room temperature. The crystal structure was solvedby direct methods and refined by the full matrix least -squares on F2 using SHELXL program package [19].All the non - hydrogen atoms were refined anisotrop-ically. The positions of the hydrogen atoms werelocated from a difference Fourier map and refinedanisotropically. The water OeH distances wererestrained to 0.82 (2) Å using DFIX option imple-mented in SHELXL program [19]. Hirshfeld surface(HS) and its two dimensional fingerprint plots werecalculated using Crystal Explorer 3.1 [20]. The Fouriertransform infrared (FTeIR) spectrum was recorded inthe spectral range 400e4000 cm�1 following KBrpellet method using PERKIN ELMER FTIR spec-trometer. UVeViseNIR transmittance spectrum of a-NSH single crystal was recorded in the wavelengthrange of 190e1100 nm using Lambda 35UVeViseNIR Spectrometer. The thermogravimetricanalysis (TGA) of a-NSH crystal was performed in thenitrogen atmosphere between the temperature range25 �C and 1200 �C using Perkin Elmer Thermalanalyzer at a heating rate of 10�C/min. The a-NSHsample weighing 8.824 mg was taken for themeasurement.

The dielectric studies on a-NSH single crystal wascarried out on the prominent (010) plane using the in-strument HIOKI 3532-50 LCR HITESTER. Theetching studies were carried out using polarized highresolution optical microscope. The third order nonlinearrefractive index (n2) and the nonlinear absorption co-efficient (b) of the grown a-NSH crystal were



calculated using Zescan technique with 20 mW laserwith wavelength of 632.8 nm and focused by a lens offocal length 12 cm. The transmitted beam through anaperture placed in the far field was measured usingphoto detector with a digital power meter. The laserdamage threshold was investigated for the well devel-oped single crystal of thickness 10 � 8 � 3 (mm3)using Qeswitched Nd: YAG laser beam.

3. Results and discussion

3.1. Single crystal Xeray diffraction and hHirshfeldsurface analysis

The crystallographic data and structure refinementparameters are given in Table 1. The ORTEP diagramof the a-NSH single crystal is shown in Fig. 3 alongwith the atomic numbering scheme. In the crystalstructure, Ni and S atoms are located in special posi-tions with half occupancy.

The Ni2þ cation has an octahedral coordination andis coordinated by six water molecules. The SO4

2� anionhas tetrahedral configuration and is coordinated by fouroxygen atoms. The selected bond lengths and bondangles are listed in Table 2. The hydrogen bonds that


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Fig. 3. ORTEP projection of a-NSH along with atom numbering

scheme; symmetry code (#) y, x, �zþ2.

Table 3

Hydrogen-bond geometry (Å,º).

DdH$$$A DeH H$$$A D$$$A DeH$$$A HS

label

O1eH1A...O2ii 0.78 (2) 2.02 (2) 2.789 (3) 170 (3) 1

O1eH1B...O5iii 0.79 (2) 1.94 (2) 2.722 (2) 171 (3) 2

O2eH2A...O5iv 0.81 (2) 2.06 (2) 2.822 (2) 159 (3) 3

O2eH2B...O4v 0.83 (2) 1.91 (2) 2.734 (3) 171 (3) 4

O3eH3A...O5vi 0.79 (2) 2.02 (2) 2.777 (2) 159 (3) 5

O3eH3B...O4 0.83 (2) 1.93 (2) 2.753 (2) 170 (3) 6

Symmetry codes: (ii) �yþ1/2, x�1/2, zþ1/4; (iii) x�1, y�1, z; (iv) y,

x�1, �zþ2; (v) x�1/2, �yþ1/2, �zþ7/4; (vi) x�1, y, z.

Fig. 4. Molecular packing viewed down the b axis. The nickel and

sulphur atoms are labelled and the hydrogen atoms have been

omitted for clarity.


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stabilize the title compound are listed in Table 3. Thecrystal packing of the title compound is illustrated inFig. 4. As shown in Fig. 4, one Ni2þ cation and oneSO4

2� anion are arranged alternately as one dimen-sional layers which run parallel to the a axis. In thislayer, distance between adjacent cations being 6.784 Å.In contrast, two cations and two anions are arrangedalternately as layers which run parallel to the c axis. Inthis layer, adjacent cations are separated by 5.716 Å.

Hirshfeld surface (HS) and its two dimensionalfingerprint plots were calculated using Crystal Ex-plorer 3.1. The intermolecular contacts with distancesequal to the sum of the van der Waals radii wereindicated as white and the contacts with distancesshorter than and longer than van der Waals radii wererepresented as red and blue, respectively on theHirshfeld surface diagram. One can easily quantify therelative contributions of various intermolecular in-teractions involved in the crystal packing using the

Table 2

Selected geometric parameters (Å,º).

Ni1eO1i 2.0085 (18) Ni1eO2 2.0822 (16)

Ni1eO1 2.0086 (18) S1eO4i 1.4702 (16)

Ni1eO3i 2.0508 (17) S1eO4 1.4702 (16)

Ni1eO3 2.0508 (17) S1eO5 1.4740 (16)

Ni1eO2i 2.0822 (16) S1eO5i 1.4740 (16)

O1ieNi1eO1 90.63 (11) O1idNi1eO2 89.56 (8)

O1ieNi1eO3i 178.55 (8) O1eNi1eO2 90.64 (8)

O1eNi1eO3i 88.11 (7) O3ieNi1eO2 91.17 (7)

O1ieNi1eO3 88.11 (7) O3eNi1eO2 88.64 (7)

O1eNi1eO3 178.55 (8) O4ieS1eO4 109.62 (14)

O3ieNi1eO3 93.15 (10) O4ieS1eO5 109.08 (11)

O1ieNi1eO2i 90.64 (8) O4eS1eO5 109.88 (10)

O1eNi1eO2i 89.56 (8) O4ieS1eO5i 109.89 (10)

O3ieNi1eO2i 88.64 (7) O4eS1eO5i 109.07 (11)

O3eNi1eO2i 91.17 (7) O5eS1eO5i 109.29 (13)

Symmetry code: (i) y, x, �zþ2.



decomposed two dimensional fingerprint (FP) plots.The FP was calculated based on the de (distance fromthe HS to the nearest atom outside the surface) and di(distance from the HS to the nearest atom inside thesurface) distances. Before calculating HS surface, theOeH distances were set to typical neutron diffractionvalues (0.983 Å). The intermolecular interactions areanalysed in detail using the HS and the importantcontacts are indicated by number (Fig. 5 and Table 3).In the crystal structure, O…H/H…O contacts are pre-dominant and the relative contribution of these inter-molecular contacts to the HS area being 66.6%. Whileintermolecular H…H contacts are contributing 32.7%to the HS area. The decomposed two dimensionalfingerprint plots are depicted in Fig. 5.

It is clearly seen from the HS analysis that the titlecompound is primarily stabilized by the intermolecularOeH…O hydrogen bonding interactions to form threedimensional networks in the solid state. All the donorand acceptor atoms in the title compound are partici-pated in the hydrogen bonding interactions. Adjacentnickel hexahydrate moieties are interconnected bysulphate anion through two intermolecular hydrogen


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Fig. 5. Different views of the Hirshfeld surfaces (a) anion and cation together (b) Nickel hexahydrate (c) sulphate anion and (d) Two dimensional

fingerprint plots. The default values are considered for colour codes (red and blue). Refer to Table 3 for HS label number.


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bonding interactions (O1eH1B…O5 and O3eH3B…O4). As shown in Fig. 6a, each of these interactionsforms an R2

2(8) ring motif [21] which runs parallel tothe b axis. Interestingly, the nickel hexahydrate moi-eties are interlinked by the intermolecular O1eH1A…O2 hydrogen bonds. This hydrogen bond generateshexameric nickel hexahydrate loop and this loop isextended further as shown in Fig. 6b. As shown inFig. 6c and Table 2, each anion is surrounded by sixnickel hexahydrate units and interconnected by inter-molecular OeH…O hydrogen bonds.

The intermolecular O2eH2A$$$O5 andO3eH2A$$$O5 hydrogen bonding interactions are

Fig. 6. (a) A chain of ring motif generated by intermolecular OeH…

O hydrogen bonds. (b) Hexameric nickel hexahydrate loop generated

by intermolecular O1eH1A…O2 hydrogen bonds. (c) Sulphate

anion is surrounded by nickel hexahydrate through intermolecular

OeH…O hydrogen bonds (symmetry code: (#) y, x, �zþ2).



acting together to produce R12(6) loop and this loop is

extended approximately perpendicular to the c axis.CCDC 1015335 contains the supplementary crystallo-graphic data for this paper. These data can be obtainedfree of charge from The Cambridge CrystallographicData Centre via www.ccdc.cam.ac.uk/data_request/cif.

3.2. FTeIR and UVeViseNIR spectral studies

The Fourier transform infrared (FTeIR) spectrumwas recorded in the spectral range 400e4000 cm�1

following KBr pellet method using PERKIN ELMERFTIR spectrometer and is shown in Fig. 7. Theobserved wavenumbers and tentative vibrational fre-quency assignment are listed in Table 4. The broadpeak occur at 3641 and 3010 cm�1 is due to asym-metric and symmetric stretching modes of water mol-ecules respectively. The vibration band observed at1667 cm�1 is assigned to d (H2O) bending vibration ofwater molecules. The strong band observed at416 cm�1 is due to the NieO stretching vibration. FreeSO4

ˉ ion has Td symmetry and has four fundamentalvibrations namely a non degenerate mode at (y1)1096 cm�1 and a doubly degenerate mode (y2)465 cm�1 and triply degenerate modes (y3 and y4) at1161 and 632 cm�1 respectively [22].

Fig. 8 shows the UVeViseNIR spectrum recordedfor a single crystal of thickness 4 mm a-NSH has threetransmittance peaks approximately centered at 300 nm,490 nm and 850 nm and at the remaining wavelengths


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http://www.ccdc.cam.ac.uk/data_request/cif

Fig. 7. FTeIR spectrum of a-NSH.

Table 4

Vibrational band assignments of a-NSH.

FTeIR (cm�1) Band assignment

3641 yas (O H)

3010 ys (O H)

1667 d (H2O)

1161 y3 (SO4)

1096 y1 (SO4)

797 yr (SO4)

632 y4 (SO4)

465 y2 (SO4)

416 NieO


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the crystal shows strong absorption. Thus the disconti-nuity in the optical transmittance at specific selectivespectral wavelengths is the required property of anycrystal to use it as band pass filter. This discontinuousspectral characteristics mainly arise from the absorption

Fig. 8. Transmittance spectra of a-NSH.



of hydrated transition metal ions Ni(H2O)62þ. The

(SO4)2- units assume regular tetrahedral geometry

which are linked with the Ni(H2O)62þ units through

OeH…O hydrogen bond. They are cross-linked toform alternating layers of octahedral and tetrahedral ashas been shown in Fig. 6b. This discontinuous trans-mission peaks of a-NSH crystal in the UV band arecomparable with those of similar type materialsK2Ni(SO4)2.6H2O, Ni(BF4)2.6H2O and NiSiF6$6H2O[11,14,15]. It can be seen from Fig. 8 that a-NSHpossesses a bandwidth in the range of 220e330 nmwhich is centered at 300 nm thereby making it a po-tential UV filter [16,20].

3.3. Thermogravimetric analysis

The decomposition process of the sample (a-NSHcrystal) takes place in three steps. The TGA curve(Fig. 9) shows no weight loss up to 110 �C.

The first step of decomposition of a-NSH starts at110 �C and ends at 300 �C resulting in a weight loss of31.32% out of the total weight of the material taken.This decomposition is due to the loss of five watermolecules. The second step of weight loss takes placebetween the temperature 300 �C and 600 �C. In thisinterval a total weight loss of 6.79% is observed.During this second stage, the removal of remaining onewater molecule takes place. The third step of decom-position is observed between the temperatures 600 �Cand 820 �C. In this step, the material gets reduced tonickel sulphite by the loss of oxygen. DSC study of a-NSH crystal, was performed using NETZSCH DSC204 differential scanning calorimeter with a heatingrate of 10�C/min at nitrogen atmosphere. For this a

Fig. 9. TGA of a-NSH.


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small piece of crystal weighing 2 mg was placed in analumina pan. The sample was scanned over the tem-perature range from 25 �C to 400 �C. The DSC plotshows three sharp endothermic peaks at 120.45 �C,131.81 �C and 159 �C as shown in Fig. 10.

3.4. Vickers's microhardness studies

Mechanical strength is the one of the importantproperties of any material concerning its use for devicefabrication. Hardness is the resistance offered by amaterial against the plastic deformation caused byscratching or indentation. The Vickers microhardnessmeasurements were carried out on a-NSH crystal usingSHIMADZU HMV - 2000 microhardness tester fittedwith a diamond pyramidal indenter. The indentationswere made at room temperature on the prominent planewith a constant dwell time of 3s. The diagonal im-pressions of the indentation marks made on the surfaceby varying load from 25 g to 200 g were measured. Toget accurate measurements for each applied load twoindentations were made and the average diagonal lengthwas used to calculate the hardness value. The Vicker'shardness number (Hv) at different loads was calculated[23] using the following relation,

Hv ¼ 1:8544P

d2

�kg

mm2

�ð1Þ

Fig. 10. DSC o



where P is the applied load in kg, 1.8544 is a constant ofa geometrical factor for the diamond pyramidal indenterand d is the average diagonal length of the indenterimpression in mm. For loads above 200 g cracks starteddeveloping around the indentation mark. The variationof microhardness values with applied load is shown inFig. 11 a-NSH crystal exhibits reverse indentation sizeeffect (RISE) in which the hardness value increaseswith the increasing load [24]. In order to analyse theRISE one needs to fit the experimental data according tothe Meyer's law.

P¼ Adn ð2Þ

where P is the applied load, A is a constant, d is theaverage diagonal length of the indenter impression inmm and n is the work hardening exponent. In the pre-sent work, the plot (Fig. 12) was drawn between log Pand log d. The work hardening coefficient (n) calculatedis 4.18. According to Onitsch [25], n lies between 1 and1.6 for hard materials and it is above 1.6 for soft ma-terials, which implies that a-NSH is a soft material.

Li and Bradt [26] explained the reverse indentationsize effect on the basis of the proportional specimenresistance (PSR) model. PSR model describes aboutthe ISE regime and load independent part. Accordingto PSR model, the indentation test is related to the loadP and the indentation size d as given below.

f a-NSH.


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Fig. 11. Microhardness behaviour of a-NSH crystal.


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P¼ a1dþ a2d2 ð3Þ

where a1 is the contribution of the PSR model to theapparent microhardness and a2 is related to the loadindependent microhardness [27]. This equation may berewritten as

P

d¼ a1 þ

�Pc

d20

�d ð4Þ

where Pc is the applied test load at which microhardnessbecomes load independent, and d0 is the diagonal length

Fig. 12. log P versus log d



of the indentation. A plot of (P/d) against d is a straightline (Fig. 13). The slope (P/d2) multiplied by Vickersconversion factor (1.8544) gives the value of load in-dependent microhardness. In the present study thecalculated load independent microhardness is 43.7 g/mm2.

3.5. Dielectric studies

A sample of dimension 10 � 10 � 4 mm3 havingsilver coating on the opposite faces was placed be-tween the two copper electrodes and thus a parallelplate capacitor was formed. The capacitance of thesample was measured by varying the frequency from50 Hz to 200 kHz. Fig. 14 shows the variation of thedielectric constant (εr) with applied frequency. Thedielectric constant is calculated using the formula

εr ¼ Ct

εoAð5Þ

where C is capacitance (farads), t the thickness (m), Athe area (m2) and (εo) the absolute permittivity in thefree space. The dielectric constant at various tempera-tures (33 �C, 50 �C, 75 �C and 100 �C) was alsomeasured. The dielectric constants possesses highvalues in the lower frequency region and then it de-creases with increase in the frequency. It was observedfrom the curve that the dielectric constant of a-NSH

for a-NSH crystal.


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Fig. 13. PSR plot of P/d versus d for a-NSH crystal.


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exhibits a normal dielectric behaviour as the dielectricconstant decreases with increasing frequency and rea-ches a constant value at high frequencies. The dielectricloss (ε00) of the crystal measured for various frequenciesat four different temperatures is shown in Fig. 15. Thehigh value of dielectric loss at low frequency region isattributed to space charge polarization due to chargedlattice defect [28]. A graph is drawn between dielectricloss and frequency for different temperatures (60 kHz,80 kHz, 100 kHz and 120 kHz). Temperature depen-dence of dielectric loss for the grown crystal at fre-quency 60 kHz, 80 kHz, 100 kHz and 120 kHz is shownin Fig. 16. Dielectric loss decreases with increase intemperature. The low value of dielectric loss at highfrequency implies that this sample possesses enhancedoptical quality with lesser defects [29].

Fig. 14. Variation of dielectric constant with log frequency.



3.6. Zescan studies

Recently interest has been focused on the study ofthird order nonlinear optical process because theyallow for the fabrication of optical devices. The mostimportant process from the point of view of opticalsignal processing is the intensity dependent phase shiftwhich results from the intensity dependent refractiveindex (n2I). Another parameter, nonlinear absorptioncoefficient, plays a major role of thermal effect whichaffects the coupling efficiency [30]. The Zescantechnique allows the simultaneous measurement ofboth the nonlinear refractive index (n2) and thenonlinear absorption coefficient (b). In this work, thesample dimension 8 mm � 10 mm � 3 mm is trans-lated in the Zedirection along the axis of a focusedGaussian beam from the HeeNe laser of 632.8 nm andthe far field intensity is measured as a function of thesample position. By moving the sample through thefocus and without placing an aperture at the detector(open aperture) one can measure the intensity depen-dent absorption of the sample. When both the methods(open and closed) are used for the measurements, theratio of the signals determines the nonlinear refractionof the sample.

The schematic setup of the Zescan technique isdepicted in Fig. 17. In open aperture method, a lensreplaces the aperture to collect the entire laser beamtransmitted through the sample. The sample causes anadditional focussing and defocusing, depending onwhether nonlinear refraction is positive or negative.The sensitivity to nonlinear refraction is entirely due tothe aperture and the removal of aperture completelyeliminates the effect. The enhanced transmission near

Fig. 15. Variation of dielectric loss with log frequency.


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Fig. 16. Variation of dielectric loss with temperature.


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the focus is the suggestive of the saturation of theabsorption at a high intensity. Absorption saturation inthe sample enhances the peak and decreases the valleyin the closed aperture Zescan. The defocusing effect isproduced due to the thermal conductivity resultingfrom the absorption of radiation of 632.8 nm. A spatialdistribution of the temperature in the crystal is pro-duced due to the absorption of focused beam propa-gating through the absorbing sample medium. Hence aspatial variation of the refractive index is produced,which acts as a thermal lens resulting in the phasedistortion of the propagating beam (Fig. 18). The dif-ference between the transmittance peak and valleytransmission (DTp-v) can be written in terms of the one axis phase shift at the focus. Table 5 shows theexperimental details of Zescan technique for a-NSH.

The on axis phase shift Dɸ at the focus can bedetermined by the relation

Fig. 17. Experimental setup



Df¼ DTp�v

0:406ð1� SÞ0:25 ð6Þ

where S is the aperture linear transmittance and is givenby the relation

S ¼ 1eexp

��2r2au2

a

�ð7Þ

where ra is the radius of aperture and ua is the beamradius at the aperture. The nonlinear refractive index(n2) is calculated using the relation [31].

n2 ¼ Df

kIoLeff

ð8Þ

where k is the wave number (k ¼ 2p/l), Io is the in-tensity of the laser beam at the focus (Z ¼ 0).

Leff ¼ 1� expð�aLÞa

ð9Þ

of Zescan technique.


j.kijoms.2016.08.002

Fig. 18. Zescan (open) spectrum of a-NSH.

Table 5

Parameters measured in Zescan experiment.

Laser beam wavelength (l) 632.8 nm

Lens focal length (f) 12 cm

Optical path distance (Z) 115 cm

Spot e size diameter in front of

the aperture (ua)

1 cm

Aperture radius (ra) 4 mm

Effective thickness (Leff) 0.99 mm

Nonlinear refractive index (n2) 3.56 � 10�9 cm2/W

Nonlinear absorption coefficient (b) 0.72074 � 10�3 m/W

Third order nonlinear susceptibility (c(3)) 7.641 � 10�7 esu


+ MODEL

where Leff is the effective thickness of the sample, a isthe linear absorption coefficient of the sample and L isthe thickness of the sample. The nonlinear absorptioncoefficient (b) is estimated from the open aperture Z escan data (Fig. 18).

b¼ 2ffiffiffi2

pDT

IoLeff

ð10Þ

whereDT is one peak value at the open aperture Zescancurve. The value of b will be negative for saturatedabsorption and positive for two photon absorption. Thereal and imaginary part of the third order nonlinearoptical susceptibility (c(3)) are defined by Ref. [32].

Recð3Þ ¼ 10�4εoc

2n2on2p

�cm2

�W� ð11Þ

Imcð3Þ ¼ 10�2εoc

2n2olb

4p2

�cm2

�W� ð12Þ

where 3o is the vacuum permittivity, c is the velocity oflight in vacuum, no is the linear refractive index of the



sample and l is the wavelength of laser beam. The thirdorder nonlinear optical susceptibility was calculatedusing the relation. Result of the Zescan study are pre-sented in Table 5.

cð3Þ ¼ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiðRecð3ÞÞ2 þ ðImcð3ÞÞ2

qð13Þ

3.7. Etching studies

Etching studies reveal the perfection of the grownsingle crystals. The etching study was carried out on the(010) face of a-NSH single crystal using doubly distilledwater as an etchant at room temperature. Polished singlecrystal was completely immersed in the distilled water.The etched samples were dried using tissue paper and thephotographswere taken using a polarized high resolutionoptical microscope fitted with motic camera. The pho-tographs were taken for the etching time of 20 s and 40 sand the pyramid shaped etch patterns obtained are shownin Fig. 19 (a) and (b) respectively. The alternate linescontaining the etch pits are observed on (010) plane. Etchpits are formed randomly on (010) plane. Whenincreasing the etching time to 40s the shape of the etchpits nearly remains the same but the etch pits diminishes.Etching studies carried out in water by Silambarasanet al. [16] on the as grown guanidine doped nickel sul-phate hexahydrate crystal for etching time of 1s showedsimilar etch pit patterns on its surface.

3.8. Laser damage threshold

Laser damage threshold (LDT) is one of the mostimportant studies because all the NLO process involvesthe ability to sustain high intensity laser light. Thesurface damage of the crystals by high power laserlimits their performance in the NLO application [33].A Q-switched Nd: YAG laser operating at 1064 nmradiation was used. The laser was operated at therepetition rate of 10 Hz with the pulse width 10s. Theout put intensity of the laser was controlled with var-iable attenuator and delivered to the test sample, whichwas located at the near focus of the converging lens.The input laser energy density was recorded using apower meter till the crystal gets damaged. The surfacedamage threshold was calculated using the formula

Power density ðPdÞ ¼ E

tpr2ð14Þ

where E is the input energy in (mJ), t is the pulse width(ns) and ‘r’ is the radius of the spot. The beam spot sizeon the sample was 660 mm and the input energy was


j.kijoms.2016.08.002

Fig. 19. Etch pits observed for various etching time in water as an etchant:(a) 20 s (b) 40 s.


+ MODEL

measured as 45 mJ. The multiple shot LDT value is1.315 GW/cm2 from the Q - switched Nd: YAG laser.Fig. 20 shows laser-induced damage pattern of growncrystal.

4. Conclusion

Slow evaporation of the solvent at room temperatureproduces transparent a-NSH single crystals. SinglecrystalXRDstudy revealed that thegrowncrystal belongsto tetragonal system. Solubility and metastable zonewidth were estimated at different temperature. Theintermolecular OeH…O hydrogen bonding interactionsstabilize the a-NSH crystal structure and form the threedimensional networks. Hirshfeld surfaces are generatedto analyse the intermolecular contacts and suggest thatO…H/H…O contacts are predominant in the a-NSHcrystal structure. The functional groups present ina-NSHcrystal are identified by FTe IR spectral analysis.UVeViseNIR spectral studies show that the a-NSHcrystal has transmission peaks at 300 nm, 490 nm and

Fig. 20. Laser laser-induced damage pattern of a-NSH.



850 nm and has higher absorption or rejection of trans-mittance in some regions which make the crystal suitablefor use in band pass UVfilter. TheVickersmicrohardnessvalue is increased with increase in the load and shows thereverse indentation size effect. Thevalue ofMeyer's indexobtained for a-NSH crystal is 4.18 which implies that thematerial belongs to soft materials category. Dielectricstudies show that dielectric loss decreaseswith increase infrequency. TGA and DSC studies reveal that the materialis thermally stable up to ~110 �C. The nonlinear opticalrefractive index n2 ¼ 3.56 � 10�9 cm2/W, nonlinear ab-sorption coefficient 0.72074� 10�3 m/Wand third ordernonlinear optical susceptibility 7.641 � 10�7 esu arecalculated by Z e scan technique. The etching studyunder different etching time carried out for the etchant ofdistilledwater indicates that higher etching timedissolvesthe etch pits. The laser damage threshold studies revealedthe grown crystal has good laser stability.

Acknowledgement

One of the authors TB acknowledge the CSIR, NewDelhi, India for providing financial support [Projectref. No. 03(1314)/14/EMR e II dt.16-04-14]. STthanks the management of SASTRA University for thefinancial support (Prof. TRR grant).

References

[1] X. Zhuang, G. Su, Y. He, G. Zheng, Cryst. Res. Technol. 41

(2006) 1031e1035.

[2] N.B. Singh, W.D. Partlow, Crystals for Ultraviolet Light Filters,

1998. US Patent No. 5788765.

[3] V. Masilamani, J. Shanthi, V. Sheelarani, Condens. Matter Phys.

5 (2014).

[4] S. Livneh, S. Selin, I. Zwieback, W. Ruderman, US Patent

6452189, 2002.

[5] E.B.Rudneva,V.L.Mamomenova,L.F.Malakhova,A.E.Voloshin,

T.N. Smirnova, J. Cryst. Growth 51 (2006) 344e347.


j.kijoms.2016.08.002

http://refhub.elsevier.com/S2405-609X(16)30079-3/sref1













+ MODEL

[6] G.B. Su, X.X. Zhuang, Y.P. He, Z.D. Li, G.F. Wang, G.H. Li,

Z.X. Huang, J. Cryst. Growth 243 (2002) 238e242.

[7] X. Wang, X.X. Zhuang, G.B. Su, Y.P. He, Opt. Mater 31 (2008)

233e236.

[8] G.B. Su, X.X. Zhuang, Y.P. He, G.Z. Zheng, Opt. Mater 30

(2008) 916e919.

[9] R.J. Harding, S.F. Mason, J. Chem. Soc. A (1970) 663e667.[10] K. Stadnicka, A.M. Glager, M. Koralewski, Acta crystallogr,

Sect. B 43 (1987) 319e325.

[11] V.L. Manomenenova, E.B. Rudneva, A.E. Voloshin,

L.V. Soboleva, A.B. Vasil’ev, B.V. Mchedlishvili, J. Cryst.

Growth 50 (2005) 877e882.

[12] R.J. Angel, L.W. Finger, Acta Crystallogr., Sect. C 44 (1988)

1869e1873.[13] C.A. Beevers, H. Lipson, Proc. R. Soc. A 148 (1935) 664e680.

[14] Youpin He, G. Su, X. Yu, Z. Li, B. Huang, R. Jang, Q. Zhao, J.

Cryst. Growth 169 (1996) 193e195.

[15] M. Hemmati, H. Rezagholipour Dizaji, Cryst. Res. Technol. 47

(2012) 703e706.

[16] A. Silambarasan, P. Rajesh, P. Ramasamy, Spectrochim. Acta,

Part A 134 (2015) 345e349.

[17] N.C.S. Kee, R.B.H. Tan, R.D. Braatz, Cryst. Growth Des. 9

(2009) 3044e3051.

[18] A.C. Zettlemoyer, Nucleation, 1969. NewYork, 243.



[19] G.M. Sheldrick, Acta crystallogr, Sect. A 64 (2008) 112e122.

[20] S.K. Wolff, D.J. Grimwood, J.J. McKinnon, M.J. Turner,

D. Jayatilaka, M.A. Spackman, Crystal Explorer (Version 3.1),

University of Western Australia, Perth, 2012.

[21] J. Bernstein, R.E. Davis, L. Shimoni, N.-L. Chang Angew,

Chem. Int. Ed. Engl. 34 (1995) 1555e1573.

[22] K. Nakamoto, Infrared and Raman Spectra of Inorganic and

Coordination Compounds, second ed., John Wiley and Sons,

New York, 1970.

[23] J. Bowman, M. Bevis, Colloid. Polym. Sci. 225 (1977)

954e966.[24] J. Gong, Y. Li, J. Mat. Sci. 35 (2000) 209e213.

[25] E.M. Onitsch, Mikroskopie 2 (1947) 131e151.

[26] H. Li, R.C. Bradt, Mat. Sci. Eng. A 142 (1991) 51e61.[27] H. Li, R.C. Bradt, J. Hard Mater 3 (1993) 403e419.

[28] K.V. Rao, A. Smakula, J. Appl. Phys. 37 (1996) 317e322.

[29] C. Balarew, R. Duhlew, J. Solid State Chem. 55 (1984) 1e6.

[30] M. Sheik Bahae, A.A. Said, T.H. Wei, D.J. Hagan, E.W. Van

Stryland, IEEE J. Quantum Electron 26 (1990) 760e769.

[31] M. Sheik Bahae, A.A. Said, E.W. Van Stryland, Opt. Lett. 14

(1989) 955e957.

[32] R.W. Boyd, Nonlinear Optics, Academic Press, London, 1992.

[33] A.J. Glass, A.H. Guenther, Appl. Opt. 12 (1973) 637e649.


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