Full Terms & Conditions of access and use can be found athttp://www.tandfonline.com/action/journalInformation?journalCode=ymri20

Materials Research Innovations

ISSN: 1432-8917 (Print) 1433-075X (Online) Journal homepage: http://www.tandfonline.com/loi/ymri20

A study on structural, compositional,microhardness and dielectric properties of LiInS2crystal

A. Arunkumar, P. Vijayakumar, M. Magesh, P. Ramasamy, E. Nageswara Rao& S. Venugopal Rao

To cite this article: A. Arunkumar, P. Vijayakumar, M. Magesh, P. Ramasamy, E.Nageswara Rao & S. Venugopal Rao (2018): A study on structural, compositional,microhardness and dielectric properties of LiInS2 crystal, Materials Research Innovations, DOI:10.1080/14328917.2018.1540456

To link to this article: https://doi.org/10.1080/14328917.2018.1540456

Published online: 29 Oct 2018.

Submit your article to this journal

View Crossmark data

A study on structural, compositional, microhardness and dielectric properties ofLiInS2 crystalA. Arunkumara, P. Vijayakumarb, M. Mageshc, P. Ramasamyb, E. Nageswara Raod and S. Venugopal Raod

aDepartment of Physics, Aurora Scientific Technology and Research Academy, Hyderabad, India; bCentre for Crystal Growth, SSN College ofEngineering, Chennai, India; cDepartment of Physics, Saveetha School of Engineering, Saveetha institute of medical and technical science,Chennai, India; dAdvanced Centre of Research in High Energy Materials, University of Hyderabad, Hyderabad, India

ABSTRACTLiInS2 material was synthesized with high purity elements in homemade graphite crucible usinghorizontal furnace. LiInS2 single crystal was grown by Bridgman method with temperature gradientof 10–15°C cm−1. The phase purity and cell parameters of grown LiInS2 crystal were confirmed bypowder x-ray diffraction and single crystal x-ray diffraction respectively. The freezing point andenthalpy of melting were found to be 977°C and 26.26 Jg−1 respectively. The compositional analysiswas made from inductively coupled plasma – optical emission spectrometry. Dielectric constant anddielectric loss was measured on (111) plane for various temperatures with frequency ranging from50 Hz to 5 MHz. The hardness of the LiInS2 single crystal in the (111) plane was assessed for differentloads. The laser damage threshold was evaluated for single shot and multiple shot at 532 nm. Thephotocurrents were measured for various temperatures with different filters.

ARTICLE HISTORYReceived 16 January 2018Accepted 28 July 2018

KEYWORDSA1. Dielectric constant; A2.From melts; B1. Nonlinearoptic materials; B2. Dielectricloss

1. Introduction

Laser plays a very important role in the modern society; toomany applications of laser in industry, medicine, military,and scientific research such as spectroscopy, microscopy,photochemistry, material processing, nuclear fusion, andso on. In order to extend laser frequency ranges, the impor-tant method, frequency conversion is often used, in whichan efficient and stable frequency-shifting device, nonlinearoptical (NLO) crystal is indispensable [1]. AIIBVICV

2 andAIBIIICVI

2 chalcopyrite semiconductors with high NLO coef-ficients, such as AgGaS2 (AGS) and ZnGeP2 (ZGP), are wellknown commercially available materials for mid-IR non-linear optics. However, these types of materials exhibitlower laser-induced damage threshold due to their narrowband gap, which limits their applications in optical para-metric oscillator (OPO) and high power laser output [2–6].Ternary chalcogenides with the general formula AIBIIICVI

2(A = Li, Na, Cu, Ag; B = Al, Ga, In; C = S, Se, Te) are ofconsiderable interest because of their potential optoelectro-nic applications such as light emitting diodes (LED), NLOdevices, detectors and solar energy converters [7]. Lithiumcontaining semiconductors are used as promising candi-dates for neutron detection and are little known becauseof difficulties of crystal growth caused by the chemicalactivities of lithium [8]. Potential advantage of the LiInS2crystals is used in frequency conversion of femtosecondpulses over all known crystals both in the mid-IR regionand in direct conversion of radiation of femtosecond Ti:sapphire (Ti:Al2O3) and Cr:forsterite(Cr:Mg2SiO4) lasersinto the mid IR region [9]. So far, many works have beenreported on crystal growth and its characterization [10–16].However, growth of LiInS2 crystal is very difficult because ofLi interaction with crucible and difficulties in handling oflithium.

The objective of present study was to grow good qualitycrystal by Bridgman method using our own designed gra-phite crucible with stepper translation. The grown crystalwas subjected to various characterizations such as powderX-ray diffraction, single crystal X-ray diffraction, differentialscanning calorimetry, ICP-OES, dielectric measurements,hardness measurement, laser damage threshold and photo-conductivity. This provides an opportunity to understandthe basic property of the LiInS2 single crystal.

2. Material and methods

2.1 Synthesis

High purity raw materials of 6N for In, 5N for S and 99.9 %for Li were used as starting elements for the synthesis. Excessof 5 % Li and 2 % S were taken for the compensation of highchemical activity of Li and evaporation loss of S at hightemperature [17]. To avoid the interaction of Li with thequartz ampoule, synthesis was performed in a speciallydesigned cylindrical shape pyrolytic carbon coated graphitecrucible, having an inner diameter 12 mm, outer diameter18 mm and length 140 mm which is shown in Figure 1. Thestarting charge materials were loaded into the graphite cru-cible using a homemade glove box under argon atmospherecondition with the humidity level of below 10%; then cruciblewas subsequently placed into a quartz ampoule. The cruciblewas sealed at residual pressure of 1.5 × 10−6 Torr.

Figure 2 shows the temperature profile of the synthesisfurnace with the sealed ampoule kept at 1080°C in the hor-izontal position. The furnace temperature was controlled by aEurotherm PID controller with K- type thermo couple. Toavoid the ampoule exploding, a stepwise temperature proce-dure was followed. The temperature was raised from roomtemperature to 400ºC (just below the boiling point 444°C of

CONTACT A. Arunkumar arunkajini@gmail.com Department of Physics, Aurora Scientific Technology and Research Academy, Chandrayangutta,Hyderabad, Telangana 500005 India

MATERIALS RESEARCH INNOVATIONShttps://doi.org/10.1080/14328917.2018.1540456

© 2018 Informa UK Limited, trading as Taylor & Francis Group

sulfur) at a rate of 30°C/h and maintained for 12 hours, 400°Cto 900°C at 20°C/h.The final temperature of 1080°C wasreached at a rate of 8°C/h and maintained for 24 hours. Atthis stage ampoule was continuously rotated with help ofmotor. Then furnace tempeature was reduced to 900 °C at arate of 15°C/h, 900°C to 400°C at a rate of 5°C/h and finally400°C to 35°C at a rate of 30°C/h. During the cooling process,ampoule explodedmany times due to prolonged Li interactionwith quartz ampoule. After several trial runs, the synthesiscondition was optimized as ampoule hot end temperatureat1080ºC and ampoule cold end temperature at 310ºC.Finally polycrystalline material was successfully synthesized.

2.2 Growth of single crystal

For crystal growth, the polycrystalline material was loadedinto bottom coned cylindrical graphite crucible under theargon atmosphere in the glove box.

The loaded graphite crucible was placed into the quartzcrucible, evacuated upto 1.5 × 10−6 Torr and then sealed.LiInS2 single crystals were grown by the modifiedBridgman-Stockbarger method in a two-zone vertical tubu-lar resistive heated furnace. In order to get the desiredtemperature gradient, a ceramic pad was introduced intothe muffle. A temperature gradient of 10–15°C/cm−1 wasobtained and maintained during crystal growth. Figure 3shows the temperature profile of growth furnace. The sealedampoule was introduced inside the vertical furnace. Theampoule was rotated at a steady rate of 3–5 rpm and theampoule was lowered at a rate of 6–12 mm/day using astepper motor. Self nucleation started at bottom tip ofgraphite crucible and crystal was grown by lowering theampoule. After complete growth, the furnace temperaturewas slowly cooled at a rate of 5°C/h to 900°C and then atthe rate of 13°C/h to room temperature. A crystal of dia-meter 8 mm and length 30 mm was grown. Twenty daystaken to complete the growth process. Many crystals weregrown by the above processes. Diamond wheel crystal cutterwas used to cut the grown LiInS2 single crystal and polishedwith a 2 μm particle size alumina powder paste (made froma mixture of alumina powder and ethylene glycol solution).Figure 4 shows as grown and the cut and polished LiInS2crystal ingots.

3. Result and discussion

3.1 Powder and single crystal X-ray diffraction

X-ray powder diffraction (XRD) is a vital tool to confirmingthe identity of a solid material and determining crystallineand phase purity. The grown crystal was ground using anagate mortar and pestle. X-ray powder diffraction analysiswas performed using a Rigaku powder X-ray diffractionsystem with the X-ray wavelength of 1.54178 Å (CuKα1)with 2θ values from 10° to 80°. X-ray powder diffractionpattern of the synthesized LiInS2 is shown in Figure 5. Thepeak positions are in good agreement with reported powderdiffraction files (PDF00-036-1352) of LiInS2.

Figure 1. Design of graphite crucible for synthesis and growth.

0 10 20 30 40 50

200

400

600

800

1000

1200

Te

mp

era

ture

(°C

)

Length (cm)

1080oC 310

oC

Figure 2. Temperature profile of the synthesis furnace with quartz crucible.

2 A. ARUNKUMAR ET AL.

The Cut and polished wafer, fabricated out of the grownLiInS2 single crystal was subjected to Powder X-ray diffrac-tion analysis. The recorded spectrum confirms the growthorientation to be <111>. The LiInS2 single crystal structure

was determined by using Enraf Nonius CAD4-MV31Bruker Kappa Apex II single crystal diffractometer.

The observed lattice parameter values are belongs toorthorhombic system are a = 6.8912(10) Å, b = 8.0591(9)

0 10 20 30 40 50

800

850

900

950

1000

1050

Tem

pera

ture

(0C

)

Length (cm)

Figure 3. Temperature profile of growth furnace.

Figure 4. (a) single crystal (b) cut and polished LiInS2.

10 20 30 40 50 60 70 80

0

200

400

600

800

1000

1200

1400

1600

(051

)(1

51)

(322

)(123

)

(320

)(3

11)(1

22)

(121

)(1

20)

(111

)(0

11)

Inte

nsity

(a.u

)

Theta/degree

(110

)

Figure 5. Powder XRD pattern for LiInS2.

MATERIALS RESEARCH INNOVATIONS 3

Å, and c = 6.4820(11) Å which is closed to the literature[18]. Figure 6 gives details about unit cell structure ofLiInS2. This structure is formed by LiS4 and InS4 tetrahe-drons, and the S2- ions are arranged in hexagonal packingwith tetragonal and octahedral cavities. It may be visualizedas a distorted tetrahedral as shown in the ORTEP view inFigure 7. The crystallographic data and the refinementdetails for LiInS2 are summarized in Table 1.

3.2 Thermo gravimetry and differential scanningcalorimetry

DSC measurements are both qualitative and quantitative;provide information about physical and chemical changesinvolved. The thermal properties of crystal have a signifi-cant influence on crystal growth and application. Thethermo gravimetry (TG) and differential scanning calori-metry were carried out using an NETZSCH STA 449F3thermal analyzer in the range 30–1000 °C at a heatingrate of 20 °Cmin−1 in the nitrogen atmosphere. In TGcurve, there is no weight loss before the melting point butweight percentage was slightly increased which might bedue to absorption of oxygen trace present in the gas used.The DSC heating and cooling curves for LiInS2 sampleare shown in Figure 8. From DSC, endothermic peak wasobserved at 1025 °C which is corresponding to the

melting point of the LiInS2. DSC cooling curves ofLiInS2 shows an exothermic sharp peak at 977°C whichis corresponding to the crystallization or solidification ofthe sample. The area under the curve corresponds to427.7 mJ. The enthalpy of melting was calculated to be26.26 Jg−1. The LiInS2 material has a congruent meltingpoint, determined by various authors as 880°C [19], 990°C [20,21], 980°C [22] 1030°C [23]. This difference in themelting point is due to the wide variation in compositionof LiInS2 crystal.

3.3 Inductively coupled plasma – optical emissionspectrometry

ICP-OES is one of the most powerful and popular ana-lytical tools for the determination of trace elementspresent in the crystal. For this analysis, the grown crys-tals were crushed into pieces and finely ground in anagate mortar. The powdered sample (16 mg) was trans-ferred into a 25 mL volumetric flask with the help of afunnel and diluted with nitric acid + deionized water.This diluted sample was analyzed by ICP-OES systemPerkin Elmer Optima 5300 DV spectrophotometer. Thecharacteristic wavelengths are observed at 670.7 nm forLi, 230.6 nm for In and 181.9 nm for S. Further, theseresults indicate that the concentrations of various ele-ments are as follows Li = 5.925 ppm, In = 94.54 ppmand S = 39.63 ppm. The atomic percent values ofLithium, Indium and Sulfur are 29.3%, 28.27% and42.43% respectively. It was observed from ICP-OES ana-lysis that the crystal has sulfur deficient. The growncrystal’s composition was Li1.17In1.13S1.7.

3.4 Dielectric measurements

For dielectric measurements, a good quality (111) planeLiInS2 crystal of 2 mm thickness was electroded on eitherside with silver paste coating to make it behave like aparallel plate capacitor. The dielectric constant and thedielectric loss of LiInS2 sample were evaluated using theconventional parallel plate capacitor method with the fre-quency range from 50 Hz to 5 MHz using the HIOKI353250 LCR HI TESTER at temperature range 30º-250ºC.

The dielectric constant was calculated using the relation.

ε0 ¼ CdAεo

(1)

ε00 ¼ ε0 tan δ (2)

Where C is the capacitance of the parallel plate capacitor,d is the thickness of the crystal, A is the area of the crystal.εo the permittivity of free space (8.85 × 10−12 C2N−1m−2).Figures 9 and 10 shows the variation of dielectric constantand dielectric loss with log frequency under different tem-peratures from 30º-250ºC. The dielectric constantdecreases very rapidly at low frequencies and slowly athigher frequencies. The electronic exchange between theions in the crystal causes local displacement of electrons inthe direction of the applied field that causes polarization.This is a normal dielectric behavior that both dielectricconstant and dielectric loss decrease with increase in fre-quency [24].

Figure 6. View of LiInS2 unit cell.

Figure 7. ORTEP view of themolecule with displacement ellipsoids drawn at 40 %.

4 A. ARUNKUMAR ET AL.

3.5 Mechanical hardness

The hardness of the material depends on different parameterssuch as lattice energy, Debye temperature, and heat of formationand inter atomic spacing [25]. During an indentation process,the external work applied by the indenter is converted to a strainenergy component which is proportional to the volume ofresultant impression and the surface energy component is pro-portional to the area of the resultant impression [26].Microhardness is a general microprobe technique for assessingthe bond strength, apart from being a measure of bulk strength.

The hardness of a material is a measure of the resis-tance it offers to local deformation. It plays a key role inthe device fabrication. The microhardness measurementwas carried out on (111) plane by using ShimadzuHMV-2 Vickers indentation tester at room temperature,and the indentation time was kept as 5 s. The Vickersmicrohardness number Hν was calculated using the rela-tion [27]

Hv ¼ 1:8544Pd2

ðMPaÞ (3)

Table 1. Crystallographic data and structure refinement parameters for LiInS2.Empirical formula LiInS2Formula weight 371.76Temperature 296(2) KWavelength 0.71073 ÅCrystal system OrthorhombicSpace group Pna21Unit cell dimensions a = 6.8912(10) Å

b = 8.0591(9) Åc = 6.4820(11) Åα = 90°β = 90°γ = 90°

Volume 359.99(9) Å3

Z 2Density (calculated) 3.430 Mg/m3

Absorption coefficient 7.441 mm−1

F(000) 336Crystal size 0.150 x 0.100 × 0.100 mm3

Theta range for data collection 3.891 to 27.996°.Index ranges −9 ≤ h ≤ 9, −10 ≤ k ≤ 10, −8 ≤ l ≤ 8Reflections collected 5955Independent reflections 868 [R(int) = 0.0309]Completeness to theta = 25.242° 100.0 %Absorption correction Semi-empirical from equivalentsMax. and min. transmission 0.7475 and 0.3937Refinement method Full-matrix least-squares on F2

Data/restraints/parameters 868/1/38Goodness-of-fit on F2 1.101Final R indices [I > 2sigma(I)] R1 = 0.0101, wR2 = 0.0215R indices (all data) R1 = 0.0129, wR2 = 0.0233Absolute structure parameter −0.03(2)Extinction coefficient 0.0334(11)Largest diff. peak and hole 0.472 and −0.346 e.Å−3

200 400 600 800 1000 120090.3

92.4

94.5

96.6

98.7

100.8

102.9

105.0

TGDSC collingDSC heating

Temperature (° C)

TG in

%

EXO

-6

-4

-2

0

2

4

6

8

mW

/mg

Figure 8. Variation of mass and heating and cooling curve of LiInS2 crystal.

MATERIALS RESEARCH INNOVATIONS 5

where P – is the indenter load and d – is the diagonal lengthof the impression.

The variation of Vickers micro hardness values with loadon the grown crystal is shown in Figure 11. Initially hard-ness number increases as load increases. There was no crackobserved upto a load of 300 g.

At a load of 500g, a significant crack developed aroundthe indentation mark, which may be due to the release ofinternal stresses generated at the corners of the indenta-tion mark. The increase in microhardness (Hv) withincreasing load is in agreement with the reverse indenta-tion size effect (RISE). The RISE can be caused by therelative predominance of nucleation and multiplication ofdislocations [28].

Various models like Mayer’s law, Hays and Kendall’sapproach, elastic/plastic deformation model and propor-tional specimen resistance model (PSR) have been proposedto explain indentation size effect phenomenon. Using PSRmodel, several researchers [29,30] have proposed that therelation may describe the normal ISE behavior

P ¼ ad þ bd2 (4)

where the parameter a characterizes the load dependence ofhardness and b is a load-independent constant. In Equation(4) when P and d are taken in N and µm, respectively, load-independent hardness Hv = 1.854b. In the present work apply-ing the PSRmodel for LiInS2 single crystal, we observed that the

2 3 4 5 6 7

0

2

4

6

8

10

30ºC 50ºC 100ºC 150ºC 200ºC 250ºC

Die

lec

tric

lo

ss

Log f (Hz)

Figure 10. Dielectric loss against log frequency for various temperatures (303–523K).

2 3 4 5 6 7

0

100

200

300

400

Log f (Hz)

30°C 50°C 100°C 150°C 200°C 250°C

Die

lectr

ic c

on

sta

nt

Figure 9. Dielectric constant against log frequency for various temperatures (303–523K).

6 A. ARUNKUMAR ET AL.

plot of P/d against d gives a straight line (Figure 12). This linearrelationship confirms that the PSR model is also applicable forexplaining the reverse ISE behavior of LiInS2 single crystal. Theconstants a and b are obtained from the plot of P/d against d forLiInS2 single crystal. In the case of LiInS2 single crystal, a is−0.007 Nµm−1. From the result of this analysis, the value of thecorrection factor a is negative. This means that in the case of thereverse ISE a specimen does not offer resistance or undergoelastic recovery as postulated in the PSR model, but undergoesrelaxation involving a release of the indentation stress away fromthe indentation site.This leads to larger indentation size andhence to a lower hardness at low loads [28].

3.6 Laser damage threshold

A nonlinear optical crystal’s ability to withstand very highpower densities of laser energy is an important factor in

various applications particularly that involves Q-switchedlasers. Hence, the determination of the laser damage thresh-old for crystal is essential as this would decide the upperlimit of the laser power density to which a crystal could beexposed. A linearly polarized second harmonic output532 nm of a Q switch Nd:YAG laser was used for thelaser damage threshold measurement. The laser was oper-ated at a repetition rate of 10 Hz, pulse duration 7 ns andbeam diameter 8 mm in TEM00 Gaussian mode. The laserpulses were focused onto LiInS2 sample by a 90 mm focallength lens, a 1 mm thick LiInS2 sample was mounted on acomputer-controlled motorized X-Y translation stage. Theoccurrence of laser damage was characterized by audiblecracking and damage was confirmed at test site by micro-scope. The measurement was made in different sites on thecrystal surface for single shot irrespective of whetherdamage had occurred on the surface or not.

0 1 2 3 4 5

400

600

800

1000

1200

1400

1600

1800

Hv

)a

PM(

Load P(N)

Figure 11. Variations of Vickers hardness number Hv against applied load P.

10 20 30 40 50 60 70 80

0.00

0.01

0.02

0.03

0.04

0.05

0.06

0.07

d/P

(N/µ

m)

d (µm)

Figure 12. P/d plotted against d for test materials.

MATERIALS RESEARCH INNOVATIONS 7

For multiple shot experiments, the same test positionwas continuously irradiated with repeated pulse of thesame intensity. The number of pulses required to makedamage on the crystal was recorded.

The diffraction limited spot diameter at focus was calcu-lated using the formula [31]

W0 ¼ 4M2λfπd

(5)

where M2 is the beam quality factor (which has a valueequal to 1 for the laser used), λ is the wavelength of the laser(532 nm), f is the focal length of the lens (90 mm) and d isthe diameter of the laser beam (8 mm). At a distance beforefocus, beam spot size was calculated by

WðXÞ ¼ W0

ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi1þ Z

ZR

� �2s

(6)

ZR ¼ πW20

λ(7)

where ZR is Rayleigh length. The spot diameter was calcu-lated to be 200 μm. The single shot surface damage thresh-old of LiInS2 crystal was measured as 70 GW/cm2. Themultiple shot damage threshold value is 45.5 GW/cm2.The multiple damage threshold value is found to be alwayslower than the single shot damage threshold value due tocumulative effects. Single shot and multiple shot damagepattern is shown in Figure 13. The star like image reflectsthe mirror symmetry of the plane of the damage. Thedominant operating mechanism is dielectric breakdown.Moreover, at the power density value slightly above thresh-old there was distorted star pattern which is shown inFigure 14.

3.7 Photoconductivity measurement

The cut and polished sample was electroded with silverpaste for photoconductivity measurement. LiInS2 crystalwas mounted in the sample holder. The photocurrent wasmeasured from 100 to 400 K under the light illuminationcondition. As the temperature increases photocurrent alsolinearly increases which could be due to the generation ofmore number of free charge carrier is observed inFigure 15. Below 250 K, photocurrent is not muchenhanced. The different filters were also employed to mea-sure the maximum photocurrent present in the crystal.Photocurrent has high response over yellow color irradia-tion and corresponding energy is 2.1eV. This energy isenough to trigger maximum electron from valence bandto conduction band. The same energy was observed intransmittance studies.

At room temperature resistivity and conductivity are cal-culated to be 1.7 × 108 Ω.cm and 5.88 × 10−9 (Ω.cm)−1

respectively. Figure 16 shows photocurrent for different filters.

4. Conclusion

The good quality IR transmittance LiInS2 single crystal wassuccessfully grown by modified Bridgman Stockbargermethod. The powder X-ray diffraction confirmed thatgrown crystal possessed phase purity. Single crystal X-raydiffraction was used to study the cell parameters. The

melting point (1025°C), crystallization point (977°C) andenthalpy of melting (26.26 Jg−1) of the LiInS2 single crystalwere measured by DSC. From ICP-OES analysis, the crys-tal composition was found to be Li1.17In1.13S1.7. The microhardness value was obtained for various loads and foundthat LiInS2 crystal undergoes reverse indentation size

(a)

(b)

Figure 13. (a) Single shot and (b) Multiple shot surface damage pattern ofLiInS2.

Figure 14. Distorted star type of multiple shot bulk damage pattern.

8 A. ARUNKUMAR ET AL.

effect. The laser damage threshold value is calculated forsingle shot and multiple shots at 532 nm.Photoconductivity was measured for different filters andvarious temperatures.

Acknowledgments

The authors thank Dr. S. Kalainathan, VIT, Vellore for providing thedielectric facility and Dr. R. Gopalakrishnan, Anna UniversityChennai for giving the hardness facility. One of the authors P.Vijayakumar thanks SSN college of Engineering for senior researchfellowship.

Disclosure statement

No potential conflict of interest was reported by the authors.

Funding

This work was supported by DRDO-NRB under [Grant no. DNRD/05/4003/NRB/185].

References

[1] Jiang X.M, Guo S.P, Zeng H.Y, Zhang M.JGuo G.C. Largecrystal growth and new crystal exploration of mid-infraredsecond-order nonlinear optical materials. Struct. Bond.2012;145:1–43.

[2] Harasaki A, Kato K. New data on the nonlinear optical con-stant, phase-matching and optical damage of AgGaS2. Jpn JAppl Phys. 1997;36:700–703.

[3] Giles NC, Bai LH, Chirila MM, et al. Infrared absorption bandsassociated with native defects in ZnGeP2. J Appl Phys.2003;93:8975.

0 10 20 30 40 500.0

0.2

0.4

0.6

0.8

100 150 200 250 300 350 4000.0

0.2

0.4

0.6

0.8

)An(tnerrucotohP

5 V 10 V 15 V 20 V 25 V 30 V 35 V 40 V 45 V 50 V

Temperature (K)

97 K 150 K 200 K 250 K 300 K 350 K 400 K

)An(tnerrucotohP

Applied Voltage (V)Figure 15. Photocurrent with applied voltage for different temperatures and inset Photocurrent with temperatures for different applied voltage.

-400 -300 -200 -100 0 100 200 300 400

-400

-200

0

200

400

600

800

DarkPhotoRedGreenBlueOrangeYellow

tnerrucotohP(µ

A)

Applied Voltage (V)Figure 16. Photocurrent with voltage for different filters.

MATERIALS RESEARCH INNOVATIONS 9

[4] Stoll K, Zondy JJ, Acef O. Fourth-harmonic generation of acontinous-wave CO2 laser by use of an AgGaSe2 and ZnGeP2doubly resonant device. Optical Letter. 1997;22:1302–1304.

[5] Lee D, Kaing T, Zondy JJ. An all diode-laser-based dual cavityAgGaS2 cw difference-frequency source for the 9-11μm range.Appl Phys B. 1998;67:363–367.

[6] Douillet A, Zondy JJ. Low-threshold, self-frequency-stablilizedAgGaS2 contnuous-wave subharmonic optical parametric oscil-lator. Optical Lett. 1998;23:1259–1261.

[7] Hua Li L, Qian Li J, Ming Wu L. Electronic structures andoptical properties of wurtzite type LiBSe2 (B=Al, Ga, In): Afirst-principles study. J Solid State Chem. 2008;181:2462.

[8] Tupitsyn E, Bhattacharya P, Rowe E, et al. Single crystal ofLiInSe2 semiconductor for neutron detector. Appl Phys Lett.2012;101:202101.

[9] Isaenko L, Yelisseyev A, Lobanov S, et al. LiInSe2: A biaxialternary chalcogenide crystal for nonlinear optical applicationsin the mid infrared. J Appl Phys. 2002;91:9475–9480.

[10] Kuriyama K, Kato T, Takahashi A. Optical band gap and blue-band emission of a LiInS2 single crystal. Phys Rev B.1992;46:15518–15519.

[11] Kuriyama K, Kato T, Takahashi A. Blue-band emission ofLiInS2 single crystals grown by the indium solution method.Jpn J Appl Phys. 1993;32(Suppl. 322–23):615–617.

[12] Kuriyama K, Kato T. Optical band gap and photoluminescencestudies in blue-band region of Zn-doped LiInS2single crystals.Solid State Commun. 1994;89:959–962.

[13] Isaenko L, Vasilyeva I, Yelisseyev A, et al. Growth and char-acterization of LiInS2 single crystals. J Cryst Growth.2000;218:313–322.

[14] Zondy -J-J, Yelisseyev A, Isaenko L, et al. New ternary sulfidefor double applications in laser schemes. In: Injeyan H, KellerU, Marshall C, editors. Advanced solid state lasers. Vol. 34.Washington D.C.: Optical Society of America; 2000. p. 561–568. (OSA Trends in Optics and Photonics Series).

[15] Knippels GM, van der Meer APG, MacLeod AM, et al. Mid-infrared (2.75–6.0 mm) second-harmonic generation in LiInS2.Opt Lett. 2001;26:617–619.

[16] Rotermund F, Petrov V, Noack F, et al. Optical parametricgeneration of femtosecond pulses up to 9 mm with LiInS2pumped at 800 nm. Appl Phys Lett. 2001;78:2623–2625.

[17] Kamijoh T, Kuriyam K. Single crystal growth of LiInS2. J CrystGrowth. 1979;46:801–803.

[18] Kuriyama K, Kato T, Takahashi A. Optical band gap and blueband emission of a LiInS2 single crystal. Phys Rev B. 1999;46:23.

[19] Boyd GD, Kasper HM, McFee JH. Linear and nonlinear opticalproperties of LiInS2. J Appl Phys. 1973;44(6):2809–2812.

[20] Kovach SK, Semrad EE, Voroshilov YV, et al. Preparation andprincipal physicochemical properties of alkali metal indates andthioindates. Inorg Mat. 1978;14(12): 1693–1697. [transl. fromIzv. Akad. Nauk SSSR: Neorganicheskie Materialy 14(12),2172–2176(1978)].

[21] Golovei MI, Peresh EY, Semrad EE. Production and character-istics of semiconductor materials of complex composition, pro-mising for quantum electronics and opto-electronics.Kvantovaya Elektronika, Kiev. 1981;20: 93–103. in Russian.

[22] Bruckner J, Kramer V, Nowak E, et al. Crystal growth andcharacterization of LiInS2. Cryst Res Technol. 1996;31(Suppl.):15–18.

[23] Badikov VV, Chizhikov VI, EfimenkoVV, et al. Optical propertiesof lithium indium selenide. Opt Mat. 2003;23(3–4):575–581.

[24] Arora SK, Patel V, Amin B, et al. Dielectric behaviour of strontiumtartrate single crystals. Bull Mater Sci. 2004;27:141–147.

[25] Dinakaran S, Jerome Dos S. Uniaxial growth of nonlinearoptical active lithium para nitrophenolate trihydrate singlecrystal. J Cryst Growth. 2008;310:410–413.

[26] Gong JJ. On the energy balance model for conventional Vickersmicrohardness testing of brittle ceramics. J Mater Sci Lett.2000;19:515.

[27] Mott BW. Micro indentation hardness testing. London:Butterworths; 1956.

[28] Sangwal K. On the reverse indentation size effect and micro-hardness measurement of solids. Materials Chem and Phys.2000;63:145.

[29] Li H, Bradt RC. The microhardness indentation load/size effectin rutile and cassiterite single crystals. J Mater Sci. 1993;28:917.

[30] Ma Q, Clarke RD. Size dependent hardness of silver singlecrystals. J Mater Res. 1995;10:853.

[31] Raghavendra Rao K, Bhat HLElizabetha Suja. Crystal growthand nonlinear optical properties of sodium d-isoascorbatemonohydrate. Crystal Engineering Communication.2013;15,:6594-6601.

10 A. ARUNKUMAR ET AL.