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1、NanoStructuredMaterials,Vol.11,No.7,pp.887±893,1999ElsevierScienceLtdPergamonCopyright©1999ActaMetallurgicaInc.PrintedintheUSA.Allrightsreserved.0965-9773/99/$±seefrontmatterPIIS0965-9773(99)00387-6GRAINGROWTHINNANOCRYSTALLINESnO2PREPAREDBYSOL-GELROUTEC
2、.H.Shek*,J.K.L.LaiandG.M.LinDepartmentofPhysicsandMaterialsScience,CityUniversityofHongKong,TatCheeAvenue,Kowloon,HongKong(ReceivedJune30,1999)(AcceptedSeptember23,1999)AbstractÐTheisothermalgraingrowthofnanocrystallineSnO2,preparedbythesol-gelroutewasi
3、nvestigatedatvarioustemperaturesbetween500°Cand800°C.Graingrowthdatawereanalyzedusingtwodifferentmodels.Aconventionalgraingrowthmodelforpolycrystallinematerialsyieldsanextremelylowactivationenergyof47kJ/mol,butlargegraingrowthexponentnfrom5to11.Theseval
4、uesexceedtherationalregiondeducedfromconventionaltheory.AnalternativemodelisbasedontheassumptionthattheorderingoftheinterfaceregionsinnanocrystallineSnO2occurssimultaneouslywithgraingrowthbystructuralrelaxation.Thisstructuralrelaxationmodeldescribestheg
5、raingrowthkineticssatisfactorilyandalsoyieldsalowactivationenergyof31kJ/molappropriatefortherearrangementofatoms.©1999ActaMetallurgicaInc.1.IntroductionNanocrystalline(nc)materialswithaveragegrainsizeoflessthan50nmhaveattractedconsiderablescientificinte
6、restbecauseoftheimprovementsinavarietyofpropertiesthatresultfromgrain-sizerefinementonthenanometerscale.Theinvestigationofthethermalstabilityorgraingrowthbehavioristhereforeimportantfromthetechnologicalpointofviewaswellasforscientificinterest.Neverthe-l
7、ess,thedynamicsofgraingrowthandtheirmechanismfornc-materialsarenotclearentirely.Thedetailedinformationespeciallyfornc-ceramicsisevenrarer.Forconventionalpolycrystallineorcoarsegrainmaterials,thedrivingforceforgraingrowthresultsfromthedecreaseofthesystem
8、energybydecreasingthetotalgrainboundaryenergy.Therateofgraingrowthisproportionaltotheradiusofcurvatureofthegrainandthekineticequationofgraingrowthis[1]:nnD2D05Kt(1)whereDistheaveragegrainsizeafterannealing,D0theinitialaveragegrai
