Author's Accepted Manuscript
Investigations on synthesis, growth and physical characterization of Lithium selenoindate
single crystals
P. Vijayakumar, M. Magesh, A. Arunkumar, G.
Anandha Babu, P. Ramasamy, K.G.M. Nair
www.elsevier.com/locate/jcrysgro
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DOI:
Reference:
S0022-0248(13)00884-1
http://dx.doi.org/10.1016/j.jcrysgro.2013.12.026
CRYS21970
To appear in:
Journal of Crystal Growth
Received date: 22 September 2013
Revised date: 11 December 2013
Accepted date: 16 December 2013
Cite this article as: P. Vijayakumar, M. Magesh, A. Arunkumar, G. Anandha
Babu, P. Ramasamy, K.G.M. Nair, Investigations on synthesis, growth and
physical characterization of Lithium selenoindate single crystals, Journal of
Crystal Growth, http://dx.doi.org/10.1016/j.jcrysgro.2013.12.026
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Investigations on synthesis, growth and physical characterization of Lithium
selenoindate single crystals
P. Vijayakumar a, M. Magesh a, A. Arunkumar a, G. Anandha Babu a, P. Ramasamy a,*,
K.G.M. Nair b
a
Centre for Crystal Growth, SSN College of Engineering, Kalavakkam-603110, Tamilnadu, India.
b
Materials Science Division, Indira Gandhi Centre for Atomic Research, Kalpakkam- 603102,
Tamilnadu, India.
Abstract
Crack free LiInSe2 single crystal with bottom dimension of 8 mm diameter and 10 mm
length and top dimension of 12 mm diameter and 22 mm length was grown using modified
vertical Bridgman-Stockbarger method with steady ampoule rotation. The grown LiInSe2 crystal
was characterized by X-ray diffraction pattern, Rutherford backscattering spectroscopy (RBS)
analysis, Thermogravimetric-Differential thermal (TG-DTA) analysis, Optical Transmission and
Microhardness measurements. X-ray diffraction pattern gives the orientation of the crystal as
<002>. RBS analysis confirms that the composition of the grown crystal is Li0.8In1.16Se2.04. TGDTA analysis confirms that the melting point of the grown crystal is 897.5 ºC. Optical behavior
has been assessed by ultraviolet-visible-Near infrared spectroscopy and Fourier transform
infrared analysis. LiInSe2 optical band gap energy is 2.72 eV and the cut off wave length is 450
nm. Mechanical behavior has been studied using Vickers Microhardness measurements.
Keywords: A1. Characterization; A1. Solidification; A2. Bridgman technique;
B1. Lithium compounds; B2. Semiconducting ternary compounds.
*Corresponding author Phone: +91-9283105760, +91-44-27475166
E-mail address: [email protected], [email protected]
1. Introduction
Crystalmaterialswhichcanworkefficientlyonthewidelytunablecoherentmidinfrared
lasersourcesintherangeof320m,speciallyinthebandof35mand814mofthe
threeatmospherictransparentwindows,aspectralrangeofimportanceforinfrared(IR)laser
technology[1],remainsacontinuingchallenge.Ternarychalcogenideswiththegeneralformula
AIBIIICVI2(A=Li,Na,Cu,Ag;B=Al,Ga,In;C=S,Se,Te)areofconsiderableinterestbecauseof
theirpotentialoptoelectronicapplicationsaslightemittingdiodes(LED),nonlinearoptical
(NLO)devices,detectorsandsolarenergyconverters[2].ThelithiumcontainingAIBIIICVI2type
semiconductorsarelittleknownbecauseofdifficultiesofcrystalgrowthcausedbythechemical
activitiesoflithiumandvolatilityofthechalcogens.However,lithiumalkalimetalternary
semiconductorsareofinterestbecausetheyhavelargerbandgapsthanthecorresponding
noblemetalcompounds.ThereisareasonthatmakestheLibasedcrystalsveryattractivefor
nonlinearoptics,AgionreplacedbylighterLiionresultsintheincreaseinthefrequenciesin
thecrystallatticevibrationsandonDebyetemperature.Itincreasesthethermalconductivity,
whichinturn,isaccompaniedbyanincreaseinopticaldamagethreshold.Particularly,LiInSe2
hasexcellentproperties,suchaswidetransparencyrange(0.4513μm),Lowerbandgap(2.86
eV),highNLOcoefficients(11.7pm/V),nearlyisotropicthermalexpansionbehaviorandbeing
phasematchableoveralargewavelengthrange[3].Mostrecently,nuclearradiationdetection
devicewasfabricatedusingverticalBridgmanmethodgrownLiInSe2singlecrystal[4].Many
authors[56]haveinvestigatedtheconditionsofgrowthofthesecrystalsbydirectional
solidificationtechnique[79].
Manyreportsareavailableforsynthesis,growthandcharacterizationofLiInSe2crystal,
howeverthereisnoreportavailableonthebasicpropertiesandcompositionalanalysis.Cecily
J.Smithet.alreportedthecompositionofreddishLiInSe2crystalpowder,howeverthe
compositiongaveastrangevariation[10]andthereisnootherreportavailableonthe
compositionsofLiInSe2.MeltandTemperatureoscillationmethod(MTOM)resultsin
homogeneouspolycrystallinematerial[1114].Basedonthese,LiInSe2polycrystallinematerial
wassynthesizedandsinglecrystalwasgrownusingmodifiedverticalBridgmanStockbarger
methodwithsteadyampoulerotation.Wehavecharacterizedthegrowncrystalforits
composition.Inthisinvestigation,wediscussthesynthesis,crystalgrowthandphysical
characterizationslikeXRaydiffractionpattern(XRD),ThermogravimetricDifferentialthermal
(TGDTA)analysis,Rutherfordbackscatteringspectroscopy(RBS)analysis,Ultravioletvisible
Nearinfrared(UVVisNIR),Fouriertransforminfrared(FTIR)spectroscopyandVickers
MicrohardnessmeasurementsofLiInSe2singlecrystals.
2.
ExperimentalSection
2.1
Synthesis
4NpurityLithium(Li),6NpurityIndium(In)and5NpuritySelenium(Se)elementswere
weighedinaccordancewiththestoichiometriccompositionof1:1:2andanexcessof5wt%Li
and1wt%SeweretakenforthecompensationofhighchemicalactivityofLiandevaporation
lossofSe.ForavoidingtheinteractionofLiwiththequartzampoule,synthesiswasperformed
inaspeciallydesignedpyrolyticcarboncoatedgraphitecrucible,havinganinsidediameter12
mmandlength140mm.Thedesignofthesynthesisandgrowthgraphitecruciblesareshownin
Fig.1(a).Thestartingmaterialswereloadedintoagraphitecrucibleusingahomemadeglove
boxunderargonatmosphere,whichwassubsequentlyloadedintoaquartzampoule.Ampoule
wassealedundervacuumat2×106millibar.Itwasthenplacedintoahorizontalfurnace,
wherethecomponentswerereacted.Duringtheheatingcycletheampoulegetsexploded,to
avoidtheampouleexplodingweincreasetheampoulevolumeandstepwisetemperature
procedurewasdesigned.Finallyweoptimisedthedimensionoftheouterampouleas19mm
innerdiameterand35mmlength.Duringsynthesis,ampouleisrotatedcontinuouslyinone
directionwith3rpmspeed.Thetemperaturegradientofthesynthesisfurnaceis8ºC/cmand
oneendoftheampouleisplacedinmaximumtemperatureof940ºCandthetemperatureof
theotherendisabout500ºC.Thetemperaturewasraisedfromroomtemperatureto680ºCat
arateof55ºC/hourandmaintainedfor12hours.Themaximumtemperatureof940ºCwas
reachedatarateof8ºC/hourandmaintainedfor24hourandreducedto800ºCatarateof
13ºC/hour.Temperatureoscillationbetween800ºCand900ºCwasexecuted.Homogenization
ofsynthesizedLiInSe2polycrystallinematerialincreaseswithincreasingnumberofoscillations.
Thetemperatureoscillationwasexecuted8times,eachoscillationhas14hoursandthenthe
meltwasslowlycooledatarateof9ºC/hourto680ºC,thentoroomtemperatureatarateof
60ºC/hour.ThesynthesizedLiInSe2polycrystallinematerialwasharvestedandnoreaction
betweenpolycrystallinematerialandgraphitecruciblewasobserved.
2.2.CrystalGrowth
Forthecrystalgrowthprocess,thepresynthesizedLiInSe2polycrystallinematerialwas
loadedintoaspeciallydesignedpyrolyticcarboncoatedconicallytaperedgraphitecrucible,
whichwasinsertedintoaquartzampoule.Ampoulewassealedundervacuumat2×106milli
bar.LiInSe2singlecrystalsweregrownbythemodiedverticalBridgmanStockbargermethod
inatwozonetubularresistiveheatedfurnace.Inordertogetthedesiredtemperature
gradient,theceramicpadwasintroducedinthemuffleandthethicknessofthepadwas
adjusted.Basedonourpreviousresultsimprovementhasbeendone.Inthisgrowthrun
12ºC/cmtemperaturegradientwasadopted.Themaximumtemperatureofthefurnacewas
slowlyraisedfromroomtemperatureto930ºCatarateof15ºC/h,andthenmaintainedfor
completegrowthrun.Theampoulewasrotatingatasteadyrateof10rpmandtheampoule
wasmechanicallydescendedatarateof12mm/dayusingsteppermotor.Whenthewhole
LiInSe2meltwassolidied,thefurnacetemperaturewasslowlycooledatarateof13ºC/hto
800ºCandthenattherateof2ºC/mintoroomtemperature.Asinglecrystalwithbottom
dimension8mmdiameterand10mmlengthandtopdimension12mmdiameterand22mm
lengthwasgrownusingagraphitecruciblewithspontaneousnucleation.ThegrownLiInSe2
singlecrystalwascutusingahomemadediamondwheelcrystalcutterandpolishedwitha1
mparticlesizealuminapowderandapastemadefromamixtureofaluminapowderand
ethyleneglycolsolution.Fig.1(b)showstemperatureprofileandinsetsshowgraphitecrucible
inevacuatedquartzampoule,grownsinglecrystalandcut&polishedwafer.
2.3.
Instrumentationforcharacterization
The LiInSe2 material phase formation and orientation of the grown crystal were identified by
X-ray diffraction (XRD) pattern using a XPERT- PRO diffractometer system. The basic
parameters are Step Size (2) 0.05°, scan step time 10.16s, scan type continuous, fixed
divergence slit type, divergence slit size 0.4785°, generator settings 30mA, 40kV, goniometer
radius 91mm, X-ray wavelength of 1.54 Å (Cu-K) along the gonio scan axis and 2 values
scanning from 10 to 80° at room temperature. Thermogravimetric-Differential thermal analysis
was carried out using a Perkin-Elmer Diamond TG-DTA instrument between the temperature
range of 30-1000ºC at a heating rate of 10ºC/min in nitrogen atmosphere. Samples were weighed
in Al2O3 crucible. The composition of LiInSe2 was determined using RBS analysis. The 1.7 MV
tandetron accelerator at IGCAR was used for carrying out RBS analysis. The RBS analysis was
carried out using both helium ions (1500 keV) and protons (1700 keV) to get the composition
information of the sample containing both light (Li) and heavy (Se, In) elements. The RBS
spectra were analyzed by SIMNRA software to obtain the composition of the sample [15]. The
optical studies were measured by Perkin-Elmer Lambda-35 spectrophotometer for the
wavelength range 200–1100 nm with slit width 2 nm and scan speed 240 nm/min, which covers
near ultra violet, visible and higher energy part of near IR region. Low energy part of near IR,
mid-IR and far-IR region was covered by the ALPHA-BRUKER spectrophotometer for the
wavenumber range 500–6000 cm-1 with an accuracy of 0.01 cm-1. Mechanical properties of the
grown crystal were studied by making indentations using MMT-X. MATSUZAWA hardness
tester fitted with a diamond pyramidal indenter and the indentation time was fixed as 5 sec.
3.
ResultandDiscussion
3.1.
XRDpattern
The X-ray diffraction pattern was done using the polycrystalline LiInSe2 which is shown in
Fig. 2 (a). The peak positions are in good agreement with the powder diffraction le (PDF card
no.04-009-0089). The Cut and polished wafer, fabricated out of the grown LiInSe2 single crystal
was subjected to X-ray diffraction analysis. The recorded spectrum (Fig. 2 (b)) confirms the
growth orientation to be <002>. Full width at half maximum of (002) peak is about 0.234º. It
indicates that the grown crystal’s perfection is reasonably good.
3.2.
TGDTAanalysis
Thethermalpropertiesofanonlinearopticalmaterialarecrucialinassessingitspotential
inrealnonlinearconversiondevicespumpedbyhighpowercontinuouswave(CW)orpulsed
lasers.TheperformanceofdevicesbasedonmidIRchalcogenidesisoftenlimitedby
deleteriousthermaleffects.TGDTAhasbeenreportedbyT.Kamijohet.alandL.Isaenkoet.al
[5,8].Howevertheyhavenotmentionedthecompositionofthecrystal.Thermalbehaviorof
thegrownLiInSe2singlecrystalhasbeenidentifiedfromTGDTAanalysisasshowninFig.3.In
theDTAcurveobtainedduringheating,anendothermicpeakstartsat881ºCandcomplete
meltingoccursat897.5ºC.Thepeakat897.5ºCcorrespondstothemeltingpointofLiInSe2.The
areaunderpeak(meltingcurve)is554.66mJandenthalpy(H)ofmeltingis51.94J/g
estimatedfromDTAanalysis.TGanalysisshowsthatthereasonableweightlossstartsat950ºC
whichindicatesthatthecompoundmeltwasstableupto950ºC.
3.3.
RBSmeasurements
RBStechniqueisapowerfultoolfortheaccuratedeterminationofcompositionofsolid
samplesanditisavaluabletoolfornondestructiveelementalanalysis.Theconcentrationsand
depthprofilesoflithium,indiumandseleniuminthegrowncrystalwereevaluatedusingthe
RBStechnique.TheRBSspectraweretakenusingprotonsandbyusingheliumbeams.
Backscatteredparticleswereobservedatascatteringangleof165ºusingasiliconbarrier
detector.Fig.4(a)andFig.4(b)showboththeexperimentalandsimulatedRBSspectrausing
SIMNRA.ThecompositioninatompercentageisLi20%,In29%andSe51%withinthe
experimentalaccuracyof±1%.ItisseenfromRBSmeasurementsthatthecrystalislithium
deficient,indiumandseleniumrich.RBSmeasurementsgivethecompositionofgrowncrystal
asLi0.8In1.16Se2.04.ThesizeofthetrivalentIndium(0.66Å)andmonovalentLithium(0.59Å)ions
areclose;thecationcationreplacementwithSeshiftintothepositionwhichisclosertothe
centeroftheemptytetrahedranispossible.InLiInSe2suchantisitedefectsareInionsintheLi
position,InLi.TheirformationiscausedbyLideficiencyaswellasbyitsstrongshiftinthe
tetrahedran.L.Isaenkoet.al.hadreportedthesameantisitedefects(InLi)inLiInS2singlecrystal
[16].Therefore,itisdeducedthatintrinsicdefectssuchasSeinterstitials(Sei)andIndiumatom
intheLithiumsites(InLi)existintheLiInSe2crystal.Thedeviationbetweenstartingcomposition
andcrystalcompositionisduetoLivapourspenetratingintothepyrolyticcarboncoated
graphitewallsandreactingwiththequartzampoulewalls.ThusLideficiencyleadsto
stiochiometricdeviation,eventhoughexcessofLiwastaken.LiInSe2singlecrystalhasLi
vacancysitesbutitwasreplacedbyindium,becauselithiummightparticipateonlyweaklyin
thecovalentbonding[17].
3.4.
UVVisNIRandFTIRspectroscopy
Thetransmissionspectrumplaysavitalroleinidentifyingthepotentialofnonlinearoptical
(NLO)materials,becauseaspecificNLOmaterialcanbeofutilityonlyifithasawide
transparencywindowwithnoabsorptionatthefundamentalandsecondharmonic
wavelengths.The2mmthickcutandpolishedLiInSe2singlecrystalswereusedfor
transmittanceandabsorptionstudiesinbothUVVisNIRandFTIRstudies.TheLiInSe2single
crystalhas22%transparencyinvisibleregionandmaximumof80%transparencyinmidIR
region.Thecutoffwavelengthisabout450nmatroomtemperature.Fig.5(a)showstheUV
VisNIRtransmittanceand(inset)absorptionspectraofLiInSe2singlecrystal.Thevalueofthe
opticalbandgapwasobtainedusingthefollowingrelationship[18]:
(h)2=k(hEg)...................(1)
whereEgistheopticalbandgap,kisaconstantandisabsorptioncoefficient.Theoptical
bandgapisdeterminedbyapplyingtheTaucmodelandtheDavisandMottmodelandisfound
tobe2.72eV.Theobtainedopticalbandgapenergyisingoodagreementwiththeprevious
report[18,19].Fig.5(b)showstheFTIRtransmittancespectrumofLiInSe2crystal.
3.5.
VickersMicrohardnessmeasurements
Indeterminingthefabricationandpossiblepracticalapplicationsthemechanicalproperties
ofmaterialsareofvitalrole[20].Hardnesstestsarecommonlyusedtodeterminethe
mechanicalpropertyofthegrowncrystals.Thisisanondestructivetestandwillquicklyyield
quantitativeinformationaboutthestrengthofthematerials.VickersMicrohardness
indentationsweremadeonthe(002)planeofthecutandpolishedwaferswiththeload
rangingfrom5gramsto100gramsusingLeitzWetzlerhardnesstester.TheVickers
Microhardnessnumberisevaluatedusingtheformula
Hv=1854P/d2(GPa)...................(2)
whereHvistheVickershardnessnumberinGPa,Pistheappliedloadinganddisthediagonal
lengthoftheindentationimpressioninμmand1854isaconstantofageometricalfactorfor
thediamondpyramid.
FromFig.6(a)itisobservedthatinitiallythehardnessincreaseswithincreaseofload.At
theselowloadstheindenterpiercesonlytopsurfacelayersresultinginincreaseofhardness
andthereafterbecomesloadindependent.Beyondtheloadof100g,asignificantcrack
developedaroundtheindentationmark,whichmaybeduetothereleaseofinternalstresses
generatedatthecornersoftheindentation.Theinitialincreaseinmicrohardness(Hv)with
increasingloadisinagreementwiththereverseindentationsizeeffect(RISE).TheRISEcanbe
causedbytherelativepredominanceofnucleationandmultiplicationofdislocations[21].
VariousmodelslikeMayer’slaw,HaysandKendall’sapproach,Elastic/Plasticdeformation
modelandProportionalspecimenresistancemodel(PSR)havebeenproposedtoexplain
indentationsizeeffectphenomenon.UsingPSRmodel,severalresearchers[2223]have
proposedthatthenormalISEbehaviormaybedescribedbytherelation
P=ad+bd2..................(3)
wheretheparameteracharacterizestheloaddependenceofhardnessandbisaload
independentconstant.TheloadindependencehardnessHv=1854b(GPa).ApplyingthePSR
modelforLiInSe2singlecrystal,weobservedthataplotofP/dagainstdgivesstraightline(Fig.
6.(b)).ThislinearrelationshipconfirmsthatthePSRmodelisalsoapplicableforexplainingthe
RISEbehaviorofLiInSe2singlecrystal.TheconstantsaandbareobtainedfromtheplotofP/d
againstdforLiInSe2singlecrystal.ThevalueofafortheLiInSe2singlecrystalindentedatlow
loadsis0.303g/μm.Thevalueofthecorrectionfactorisnegative.Thismeansthatinthecase
oftheRISEaspecimendoesnotofferresistanceorundergoelasticrecoveryaspostulatedin
thePSRmodel,butundergoesrelaxationinvolvingareleaseoftheindentationstressaway
fromtheindentationsite.Thisleadstoalargerindentationsizeandhencetoalowerhardness
atlowloads[21].
4.
Conclusion
MTOMwasusedtosynthesiseLiInSe2polycrystallinematerial.CrackfreeLiInSe2single
crystalwithbottomdimensionof8mmdiameterand10mmlengthandtopdimensionof12
mmdiameterand22mmlengthhasbeengrownusingasteadyampoulerotationbymodified
verticalBridgmanStockbargermethod.TheLiInSe2crystalisgrownalongthe<002>direction.
TGDTAanalysisconfirmsthatthemeltingpointofthegrowncrystalis897.5ºC.RBSanalysis
confirmsthegrowncrystalcompositionasLi0.8In1.16Se2.04.TheresultshowedthatLiInSe2crystal
grownusingtheMTOMsynthesizedpolycrystallinematerialshadreasonablygood
stoichiometriccomposition.Opticalstudiesrevealthatthetransmissionregionisstartingfrom
450nmandopticalbandgapenergyis2.72eV.FTIRanalysisgivesthemaximumof80%
transparencyinmidIRregion.Themocrohardnessmeasurementson(002)planeshowreverse
indentationsizeeffectinLiInSe2singlecrystal.
Acknowledgements
ThisworkwassupportedbyDRDONRBunderGrantno.NRD/05/4003/NRB/185.
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Figure captions
Fig. 1. (a) Graphite crucible design for (i) Synthesis & (ii) Growth, (b) Temperature profile for
growth and (inset) graphite crucible in evacuated quartz ampoule, grown single crystal and cut &
polished wafer of LiInSe2
Fig. 2. PXRD pattern of the polycrystalline and (inset) grown LiInSe2 single crystal
Fig. 3. TG-DTA spectrum of the grown LiInSe2 single crystal
Fig. 4. RBS experimental and simulated spectrum of the LiInSe2 wafer using (a) 1500 keV
helium ions and (b) 1700 keV protons.
Fig. 5. (a). UV-Vis-NIR Transmittance and (inset) absorbance spectrum and (b) FTIR
Transmittance spectrum of the LiInSe2 wafer.
Fig. 6. Plot of Load (P) Vs Microhardness (Hv) and inset plot of d Vs P/d for LiInSe2 crystal
(002) plane.
Research highlights
¾ Melt and Temperature Oscillation Method was adopted for synthesizing LiInSe2
¾ The large LiInSe2 crystal of high integrity was grown by the modified VerticalBridgman- Stockbarger method
¾ RBS measurement confirms the composition of the LiInSe2
¾ PSR model is applied for hardness measurements
(a)
(b)
15
100
10
20
30
2 T (degree)
40
16
10
50
20
30
60
40
(053)
(113)
Intensity (a.u)
(123)
450
(333)
(322)
(231)
400
(431)
(013)
(130)
(122)
(212)
(210)
200
(112)
(120)
300
(002)
(011)
500
(111)
(110)
Intensity (a.u)
600
(002)
400
350
300
250
200
150
100
2 T (degree)
50
60
70
70
80
0
80
10.8
5
10.7
0
10.6
-5
Weight (mg)
10.5
-10
10.4
-15
10.3
10.2
-20
10.1
o
897.5 ( C)
-25
10.0
0
100
200
300
400
500
600
o
Temperature ( C)
17
700
800
900
1000
Microvolt endodown (PV)
TG
DTA
(a)
(b)
18
25
95
(a)
(b)
90
20
Transmittance (%)
4
10
3
Absorbance %
Transmittance (%)
85
15
5
65
400
500
600
700
800
900
1000
1100
Wavelength (nm)
200
300
400
500
600
75
70
2
1
0
80
700
800
900
60
1000
1100
1000
2000
3000
4000
5000
-1
Wavelength (nm)
Wave Number (cm )
19
6000
1.1
25
20
0.9
15
-3
P/d (x10 N/ Pm)
Hv (GPa)
1.0
0.8
10
5
0.7
10
15
20
25
30
35
40
d (Pm)
0
20
40
60
Load P (g)
20
80
100