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2.3.TechniquesofGrowthofSelectedBinaryandTernaryOxideCrystals
37
Owingtoauniformtemperaturedistributionandtheprecisetemperature
controlofthedietoptheribboncrystalexhibitednograinboundaries.
InthegrowthofcrystalswithhighmeltingtemperaturesuchasTiO
2,heat
transferismainlybyradiation.Theabsorptioninthegrowingcrystalwould
haveaconsiderableinfluenceontheheattransferandthegrowthstability
[16].Itwasfoundthatbulkrutilecrystals,whichweredimculttogrow
usingtheCzochralskitechnique,couldbesuccessfullygrownusingthe
EFGmethod.Therutilecrystals,justaftertheystartgrowing,arereduced.
Inthisway,asitwasmentionedabove,itchangesheattransportandcaus-
esabruptlateralgrowthoftherutilecrystalswhenthemelttemperature
decreasesinCzochralskigrowth.InthecaseofEFGgrowth,thecrystal
shapeislimitedbythedieedgeandthemeniscusheightonthedietopis
short.Therefore,itisquitenaturalthatthecrystalshapecontrolismuch
easierusingtheEFGmethodcomparedwiththeCzochralskimethod.Ad-
ditionally,theuniformityofthetemperaturedistributionattheEFGgrowth
interfaceisthegoodduetotherelativelysmallradialtemperaturegradient
causedbygoodthermalconductivityofthedie.Auniformrutileboule,
15mmindiameterand40mminlengthwasgrownundermodifiedEFG
conditionswithoutcrystalrotation[17].TheEFGmethodwasalsousedto
growcylindricalSrTiO
3bulksinglecrystalswithdiametersofabout15mm
andlengthsupto50mmfromstoichiometricmelts.Typicalaverageetch
pitdensityvalueswereintherangeof1.7-2.0×10
5cm-2.Rockingcurve
measurementsrevealedFWHMvaluesbetween28!!and41!![14].
Thefloatingzone(FZ)methodallowsbothcrystallizationfromstoichi-
ometricmeltsaswellascrystallizationwiththeuseoftravelingsolvent.
Inthecaseofoxidescrystallizationinfra-redIRheating(IR-FZ)isused.
AtypicalfurnacefortheIR-FZmethodisasingle-ellipsoidal-mirror-type
imagefurnace,buttwo-orevenfour-ellipsoidal-mirror-typeimagefur-
nacesarealsoused,givingmoreuniformheating.Theshapeofthemolten
zonemaybeinfluencedusingatiltingmirrortypeimagefurnace.Byprop-
erlychosenthermalconditionstheconvexityofthecrystal-sideinterface
maybedecreasedandstabilityofthemoltenzonemaybeincreased.The
qualityofrutilesinglecrystalsgrownbymeansofthistechniquewasim-
proved.Alargerutilesinglecrystalof19mmdiameterwassuccessfully
grownunderthemirrortiltedconditions[18].FZmethodwasalsoused
togrowgoodqualitysinglecrystalsofSrTiO
315-20mmindiameterand
40-80mminlength.Additionalcrystalheatingjustbelowthemoltenzone
byanin-growthannealingfurnacewasappliedinordertolowerthetem-
peraturegradientsandtoachieveslowercoolingofthegrowncrystal.The
crystalperfectionwasstudiedwithX-raytopographyanddouble-crystal