Decomposition reactions in CaCu3Ti4O12 ceramics

Journal

J.Am.Ceram.Soc.,89[9]2833–2838(2006)

DOI:10.1111/j.1551-2916.2006.01174.xr2006TheAmericanCeramicSociety

DecompositionReactionsinCaCu3Ti4O12Ceramics

TimothyB.Adams,DerekC.Sinclair,wandAnthonyR.West

DepartmentofEngineeringMaterials,TheUniversityofShef eld,MappinStreetS13JD,U.K.

CaCu3Ti4O12(CCTO)ceramicssinteredinairat11151Cfor3and24hhavebeenheattreatedinN2at10001C.Surfacelayersdevelopontheouterregionsoftheceramics,andacombinationofX-raydiffractionandanalyticalelectronmicroscopyhasbeenusedtoestablishthephasecontentofthelayers.AmodeltoexplaintheformationofthesurfacelayersisproposedbasedondecompositionofCCTOintoamixtureofCaTiO3,TiO2,andCu2O.TheroleoflimiteddecompositioninthedevelopmentofelectricallyinhomogeneousCCTOceramicspreparedatelevat-edtemperaturesinairisdiscussed.

I.Introduction

iscurrentlyconsiderableinterestinanunusualper-ovskite-relatedoxideCaCu3Ti4O12(CCTO)1–3asapoten-tialmaterialforinternalbarrierlayercapacitor(IBLC)applications.ItisnowgenerallyacceptedthatCCTOceramicspreparedinairat410001Careelectricallyheterogeneous,con-sistingofn-typesemiconductinggrainsandinsulatinggrainboundaries,3–5therebypossessingtherequiredelectricalmicro-structureofanIBLC.TheadvantageofCCTOcomparedwithothertitanateperovskitessuchas(Ba,Sr)TiO3-basedceramics(BST)forIBLCapplicationsisthattheelectricalmicrostructurecanbedevelopedinasingleprocessingstepinairandthereforeavoidthemulti-stepprocessingroutesrequiredforBST.Thedefectchemistryandmicrostructuraldevelopmentassociatedwiththemulti-stepprocessingrouteofBSTceramicsisnowreasonablywellunderstoodandhasbeendevelopedovermanyyearstooptimizetheIBLCcharacteristicsofthesematerials.Incontrast,thedefectchemistryandevolutionofceramicmicro-structureofCCTOremainpoorlyunderstood.Establishingtheoriginofthen-typesemiconductivityinCCTOandthecompo-sitionofthegrainboundaryregionsinCCTOceramicsremainchallengingandimportantproblems,especiallyifthesematerialsaretobeoptimizedforIBLCorrelatedapplicationsinthenearfuture.

Twomodelshavebeenproposedforthen-typesemicon-ductivityinCCTO.The rstinvolvesoxygenloss,viz.,CaCu3Ti4O12Àd,asiscommonlyobservedformanytitanate-basedperovskitessuchasBST6whenheatedathightempera-turesand/orunderreducingatmospheres.Althoughthelevelofoxygenlossisoftensmall,d(0.01,itissuf cienttochangeelectricallyinsulatingTi-basedperovskitessuchasBSTfromanoff-white/creamcolorwithabulkresistivityinexcessof1010OÁcmatroomtemperature(RT),intoadark-bluecolorwithanRTbulkresistivityB0.1–10OÁcm.Thebluecolorandn-typesemiconductivityareduetopartialreductionofTi41(do)toTi31(d1)associatedwiththeoxygenlossfromthelattice.

TO

HERE

T

ceramicsarecommonlysinteredintherangeB10001–11001C,andtherefore,inthismodel,reductionofCu21toCu1occursatthesehightemperatureswithchargecompensationbypartialoccupationoftheCusitebyTi41accordingtotheformula

1141

Ca(Cu21À3xCu2xTix)3Ti4O12.OncoolingtoRT,themonovalentCu1ionsarere-oxidizedtoCu21ionsandaninternalredoxprocessoccurs,causingpartialreductionofTi41toTi31ionsontheB-sitesublatticeleadingtotheformula

1414131

Ca(Cu21ÀxTix)3Ti4À6xTi6xO12,andn-typesemiconductivity.AshasbeenpointedoutbyLietal.,7onlysmalllevelsofei-theroxygennon-stoichiometry(model1)orcationnon-stoic-hiometry(model2),xo0.001,arerequiredtoinducethelevelofRTbulksemiconductivity(B10–100OÁcm)commonlyob-servedforCCTOceramics.Itisthereforelikelytobeverydif- culttodistinguishbetweenthesetwomodelsbydirectchemicalanalysis;however,someformofCu-richsecondaryphase(s)shouldbedetectedformodel2insamplespreparedfromastartingcompositionofstoichiometricCaCu3Ti4O12,assumingnegligiblevolatilityofCuathightemperatures.

Recently,wehavereportedelectronprobemicroanaly-sis(EPMA)onCCTOceramicssinteredfor24hinairat11151C.8TheresultsrevealedthepresenceofCu2Owithintheceramicsandmoresignificantly,theCCTOgrainstobeCude- cientwithanaveragecompositionCa0.98(2)Cu2.92(2)Ti4.04(2)O12(onlycationcontentsweredetermined).Inaddition,dramaticchangesinphaseassemblagewereobservedforCCTOceramicsheattreatedinN2at48001Cwiththedevelopmentofsurfacelayers.ImpedancespectroscopywasusedtoshowedthattheRTbulkresistivityofB100OÁcmobservedinCCTOceramicssin-teredinairwasinsensitivetoheattreatmentinN2orO2at8001–10001C.9Incontrast,theRTgrainboundaryresistanceshowedsubstantialvariationwithpost-heattreatment,decreasingbythreetofourordersofmagnitudeafterheattreatmentinN2.9Theresistanceofthegrainboundariescouldberecoveredtovaluesclosetotheair-sinteredvalueswhenheattreatedinO2at10001C.TheseresultshaveledustosuggestthatoriginofthesemiconductivityinCCTOismoreprobablyrelatedtocationnon-stoichiometry(model2)thantooxygenloss(model1).Tothebestofourknowledge,thethermalstabilityofCCTOceramicsundervariousheat-treatmentconditions(temperatureandoxygenpartialpressure)hasnotbeenestablished.Here,wereportphaseanalysisbyX-raydiffraction(XRD),thermalanal-ysis,andanalyticalelectronmicroscopyresultsonCCTOce-ramicsthathavebeensinteredinairat11151Candthenheattreatedinaninert( owingN2)orreducing( owing5%H2/95%Ar)atmosphereat10001C.CharacterizationofthesurfacelayersthatdeveloponCCTOceramicsundertheinertcondi-tionsprovidesfurtherinsightsintotheimportantroleofthein-stabilityofCu21inCCTOceramicssinteredinairathightemperatures.

II.ExperimentalProcedure

D.Johnson—contributingeditor

ManuscriptNo.21586.ReceivedMarch14,2006;approvedMay4,2006.WethanktheEPSRCfor nancialsupport.w

Authortowhomcorrespondenceshouldbeaddressed.e-maild.c.sinclair@Shef eld.ac.uk

High-purityCaCO3,CuO,andTiO2reagents(all99.99%pure,AldrichChemicalCo.,Milwaukee,WI)atamolarratioof1:3:4weremixedinaplanetaryballmill(FritschGMBHmodelpul-verisette6,Albishein,Germany)withacetoneusinganagatepotandballs(amixtureof5and10mmballs)at250rpmfor20min.Afterdrying,thepowder(B10g)wasreactedinairover-

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nightat10001ConaPtfoilandthenmilledagainat250rpmfor30minbeforeasecondreactionat10001C.Thepowderwasthenplanetaryballmilledat250rpmfor60min.

XRDwasperformedonpowdersamplesusingahigh-reso-lutiondiffractometer(StoeStadiP,StoeandCieGmbH,Dar-mstadt,Germany)operatedat50kVand30mA(stepsizeofscan0.021andscanrate21/min)toassessphasepurity.XRDonpelletsurfaceswasperformedusingaSiemens(Karlsruhe,Germany)X-raydiffractometerwithCuKa1radiation.Particlesizeanalysis(ModelCoulterLS130,Beckmann,HighWyco-mbe,UK)showedabimodalparticlesizedistributioninthepowderatB0.4and6mmandad50valueofB3.4mm.

CaCu3Ti4O12powdercompactswerepressedina10mmsteeldieat0.5tonandsinteredat11151Cinairforeither3or24h,andfurnacecooledtoRT.Pelletdensitieswerecalculatedfromthemassanddimensionsofthepelletsandallwere495%ofthetheoreticaldensity.

Ceramicsforscanningelectronmicroscopy(SEM)werepre-paredbymountinginresinandpolishingsectionsperpendiculartothemajorpelletfaces.ThepolishedceramicswerecarboncoatedandanalyzedusingaJEOLJSM-6400SEM(JeolLtd.,Tokyo,Japan)equippedwithaLINKenergy-dispersiveX-ray(EDS)detectorandancillaryelectronicsoperatingat20kV.Theas-sinteredsurfaceof24hceramicswasanalyzedbyXRD,andthenpolishedwithSiCpaperandre-measured;theprocesswasrepeateduntilthesamplewasB80%oftheoriginalthickness.Theceramicmicrostructuresofpelletssinteredfor3and24hconsistofaveragegrainsizesofB5and4100mm,respectively.Detailsoftheceramicmicrostructureshavebeenreportedpreviously.4

Hydrogen-reductionthermogravimetry(TG)in5%H2/95%Ar(heatingrate101C/min,referenceAl2O3)wasperformedonpowder(B50mg)fromacrushed24hpellet.

As-sintered3and24hceramicswereplacedonaPtfoil,in-sertedintoatubefurnace,andheattreatedinoxygen-freeN2for6hat10001C(heatingrate51C/min,coolingrate2.51C/min).A3hheat-treatedceramicwasanalyzedbyXRDasafunctionof

pelletthicknessasdescribedabove.Finally,samplesof3and24hheat-treatedceramicswerepreparedforSEMasdescribedabove.

III.ResultsandDiscussion

Low-andhigh-magni cationbackscatteredelectronimages(BEI)ofas-sintered3and24hceramics,viewedasacrosssec-tionperpendiculartothemajorpelletfaces,areshowninFig.1.Atlowmagni cation,the3hsampleappearshomogeneouswithoutlarge-scale aws,suchas ssures,orporesover5mmindiameter,Fig.1(a),whereasthe24hsamplerevealsacoarserporestructurewithporesizesupto30mm,Fig.1(b).Athighermagni cationa ne-grainedtexture(o10mminsize)isevidentforthe3hsample,andtheporestructure,observedasblackvoids,isclosed.Asecondaryphasewasobservedasbrightpre-cipitatesinanumberofporesand,inparticular,atgrainbound-aryjunctions,Fig.1(c).Thegrainstructureofthe24hsamplewasmuchcoarser,althoughitwasnotpossibletoassessaccu-ratelyasthesampleswerenotetched,butpreviousresultshaveshownthatthegrainsaretypicallybetween100and300mminsize.4Asecondaryphasewasdetectedasbrightprecipitatesus-ingBEI,Fig.1(d),consistentwiththatobservedforthe3hce-ramic.Anadditionalsecondaryphaseforthe24hsamplewasobservedinBEIasdarksphericalprecipitatesofB5mmdiam-eter,Fig.1(d).

AtypicalEDSspectrumofthemainCCTOphaseinboth3and24hsamplesisshowninFig.2.Theobservedpeakscor-respondtoknownpeakpositionsforCa,Cu,andTi.AlthoughtheEDSdatadonotprovideadirectmeanstoquantifythecompositionofaparticularregion,thedataarerepresentativeofthebulkCaCu3Ti4O12phase,consistentwithanalysisperformedbyEPMAandreportedpreviously.8Figure2(b)showstypicalEDSdataforthebrightphaseobservedatthegrainboundaryjunctionsinthesamples.ThetwomajorpeakscorrespondtoknownpeakpositionsforCuandarecommensuratewith

the

Fig.1.Backscatteredelectronimagesscanningelectronmicroscopyshowingcrosssectionsof(a)3hand(b)24hCaCu3Ti4O12ceramicsatlowmagni cationandhighmagni cation(candd,respectively).

September2006DecompositionReactionsinCaCu3Ti4O12Ceramics2835

Fig.2.Typicalenergy-dispersiveX-rayspectraof(a)bulkCaCu3-Ti4O12phaseandsecondaryphasesobservedbybackscatteredelectronimagesas(b)brightprecipitatesand(c)darksphericalprecipitates.

Cu2Ophase,alsodetectedbyEPMA.8ThesecondarypeakscorrespondtoSi,Ca,andTi,whichmayarisefromtheprecip-itateitself,orfromsurroundingmaterialiftheinteractionvol-umeexceedsthevolumeoftheprecipitateduringtheEDSanalysis.TheEDSdatainFig.2(c)aretypicalofthedarkphaseobservedinthe24hsample,withmajorpeakscorrespondingtoSi,Ca,andTi,andaminorpeakcorrespondingtoCu.Themorphologyandcomposition(accordingtotheEDSdata)areconsistentwithCaTiSiO5(sphene)precipitatesobservedbyEPMA,asreportedpreviously.8TheCusignalmayarisefromincorporationofCuintothesphenelatticeorasaresultofin-teractionoftheprimarybeamwiththesurroundingarea.ThepresenceofSiarisesduetounintentionalcontaminationfromthemillingmediausedinthepowderprocessing.

RepresentativeXRDdataforas-sinteredandpolishedsurfacesofCCTOceramicspreparedinairat11151CareshowninFig.3.Allre ectionsfromtheas-sinteredpelletsurfacewiththeexceptionofasmallpeakatB36.51correspondtothepatternreportedintheliterature10andICDDcardnumber75-2188forCaCutheas-sintered3Ti4O12.TheadditionalminorpeakobservedatB36.51inpelletsurface(seetheinsetinFig.3)wasremovedonpolishingthepelletsurfacesandmaycorre-spondtoCu2OprecipitatesatthesurfaceasthemostintensepeakintheXRDpatternforCuthe(111)re ectionat36.5212O(ICDDcardnumber77-199)is1.Unfortunately,thesecondmostintensepeak(200re ection)forCu2Ooccursat42.4231,whichisclosetothe(111)re ectionforCCTO;seetheinsetinoFig.3.AllremainingpeaksforCu2Ophase,30%,whichandgivenwaslimitedthesmallonlyvolumetotheas-sinteredfractionhaverelativeofintensitypellettheimpuritysurface,

Fig.3.TypicalX-raydiffractionpatternsobtainedfromanas-sinteredpelletsurface(bottomtrace)andthen,sequentially,fromlayer-by-layerpolishedpelletsurfaces(upper

traces).

itisnotpossibletoattributeunequivocallytheextrare ectiontoCuLow-magni cation2O.

BEIimagesof3and24hsamplesheattreatedinN2for6hat10001CareshowninFig.4.TheimagecontrastrevealstwocompositionallydistinctlayerssurroundingthebulkCaCu3Ti4O12materialinbothsamples;theselayersappeartoforma‘‘decompositionzone,’’Fig.4(a)and(b).Ahighermagni cationimagefora3hsampleshowstheinterfacebetweentheoutertwolayers,Fig.4(c)(asimilarimage,notshown,wasobtainedfora24hsample)andtheinterfacebetweentheinnerlayerandbulkmaterial,Figs.4(d)and(e).Theoutermostlayerwasahighlyporous(B50%dense),‘‘coral-like’’structureofB1mmdiameterinterconnectedstrands.Thisstructureformsthematrixofaninnerlayerinwhichtheporesare lledwithaphasethatappearsbrighterthanthematrix.Inbothsamples,thethicknessofthelayersvariesgreatlysuchthat,for3hsamples,theouterlayercanextendB100mmintothesampleor,conversely,theinnerlayercanextendfromthebulkinterface,throughtheouterlayerandtothepelletsurface.Theoverallthicknessofthedecompositionzonewasrelativelyconstantinbothsamples.Forthe3hsample,thedecompositionzonethicknesswasB150mmatthemajorpelletfaces,increasingtoB200–300mmalongthepelletcircumfer-ence.B100–150ThedecompositionTypicalEDSmm.

zonewasthinnerinthe24hsample,dataforthebrightprecipitatephaseandmatrixphaseobservedinthedecompositionzoneareshowninFigs.5(a)and(b),respectively.Thebrightphasecorrespondstoacopper-richphase,whichiscon rmedbyXRD(seelater)tobeCu2O.ThepresenceofCaandTiintheEDSdatamay,asbe-fore,arisefromtheirincorporationintotheCu2Olatticeand/orfrombeaminteractionswithsurroundingmaterial.ThedarkmatrixcontainsCa,Ti,andSi,andXRD(seelater)isusedtoshowevidenceofseveralphases,includingCaTiO3andTiO2.Forbothsamples,theinterfacebetweentheinnerlayerandthebulkmaterial,Figs.4(d)–(e),isclearlyde nedbya netex-tureofCuand,below2OstriationsoriginatingfromtheCaCutheinterface,themicrostructureiscomparable3Ti4O12grainsbothintermsofgrainsize,porosity,anddistributionofsecondaryphase(s)tothatoftheas-sinteredsamplesinFig.1.Thetextureisclearlylessstriatedinthe3hsample,suchthatthestriationsextendfor5–10mmbeforecoalescingintoamore‘‘globular’’morphology,Fig.4(d).Theinnerlayerofthe24hsample,how-ever,wasentirelystriatedbetweentheinterfacewiththeouterlayerandtheinterfacewiththebulkmaterial,Fig.4(e).

ThecrystallinephasescontainedwithinthedecompositionzoneandthebulkmaterialforsamplesheattreatedinN1CwerecharacterizedbyXRD;layer-by-layerand

typical

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Fig.4.Low-magni cationbackscatteredelectronimagesscanningelectronmicroscopy(BEISEM)of(a)3hand(b)24hsamplesincrosssectionafterheattreatmentat10001CinN2.BEISEMshowinginterfacebetweentheouterlayerandtheinnerlayerofthedecompositionzonein(c)3hsampleafterheattreatmentat10001CinN2.BEISEMshowinginterfacebetweenthebulkphaseandtheinnerlayerofthedecompositionzoneof(d)3hand(e)24hsamples.

resultsareshowninFig.6.As-sinteredCaCu3Ti4O12pelletswereblackincolor,whereasthoseheattreatedat10001CinN2werewhite.Lightpolishingofthepelletsurfacesoftheheat-treatedsamplesresultedinasequenceofcolorchangesfromwhitetoorange,thendarkbrown,and nallyblack.Thesechangesaremacroscopicevidencefortheexistenceofthetwolayersinthedecompositionzoneandthebulkmaterialbelow,asobservedbySEM.XRDdatawereobtainedfromthevariouscoloredpelletsurfaces,assummarizedinFig.6.ThebottomtraceinFig.6showstheXRDdatafortheoriginalwhitesur-face,andsubsequentdatasetsarefortheorangesurface(layer1),darkbrownsurface(layer2),and nallytheblacksurface(layer3andbulk).

Re ectionsobservedfromthewhitesurfacecorrespondtoTiO2(rutile),(ICDDcard21-1276)andCaTiO3(ICDDcard22-153),inagreementwithEDSdataobtainedfromtheouterlayerandinnerlayermatrix.ThereisnoevidenceofCaCu3Ti4O12oranycrystallineCu-containingoxides.Inaddition,therewasnoevidenceforspheneorcrystallineSiO2intheXRDdata,sug-gestingthattheSidetectedbyEDSwaseitherpresentinanamorphoussilicatephaseorincorporatedintotheTiO2and/orCaTiO3lattice,orinsuchsmallquantitiesthatitcouldnotbedetectedbylaboratoryXRD.Thechangeinpelletsurfacecolorfromwhitetoorangecoincideswiththeobservationofextrare ectionscorrespondingtoCu2O(Fig.6,layer1).Thisismostclearlyobservedbytheappearanceofthe(311)re ectionatB73.71forCu2O;unfortunately,themostintensepeakforCu2O,atB36.51,the(111)re ection,occursinthevicinityofthesecondmostintensepeak,(101)re ection,forrutile.Thiscon rmsthemajorprecipitatephaseoftheinnerlayertobeCu2O,andtheouterlayer‘‘coral’’structureofTiO2andCaTiO3alsoformsthematrixoftheinnerlayer.Furtherpolishing,untilthechangeincolorfromorangetodarkbrown,yieldedre ec-tionsintheXRDpatterncorrespondingtoCaCu3Ti4O12,Cu2O,TiO2,andCaTiO3(Fig.6,layer2).Afterfurtherpolishing,allre ectionswerefoundtocorrespondtoCaCu3Ti4O12(Fig.6,layer3andbulk).

HydrogenreductionTGwasperformedonasmallamountofpowderfromacrushedpelletsinteredinairat11151Cfor24h.WeightlosscommencedatB3301Candwascomplete

by

September2006DecompositionReactionsinCaCu3Ti4O12Ceramics2837

Fig.5.Typicalenergy-dispersiveX-rayspectrafrom(a)thebrightpre-cipitatephaseintheinnerlayerofthedecompositionzoneand(b)thematrixphaseintheinnerandouter

layer.

Bpowder6801C,followingwithatotalthemassTGlossexperimentofB8%.revealedXRDofnothetraceremainingoftheoriginalCCTOphase.Instead,thesampleconsistedofCaTiO3,TiO2(Rutile),andmetallicCu,Fig.7,indicatingcompletede-compositionofCCTO.TheobservedmasslossofB8%2is1ingoodagreementwiththatexpectedforthereductionofCutoCumetal(7.8%massloss)foraninitialstartingcompositionofCaCu3Ti4O12.AlthoughitisclearthatCCTOceramicsarein-homogeneous,theoveralldecompositionprocessinreducingconditionscanbedescribedbythefollowingequation:

CaCu3Ti4O12!CaTiO3þ3TiO2þ3Cu

þ3=2O2ðgÞ

(1)

ThedecompositionprocessoccurringinCCTOceramicsat10001CinN2isincomplete,presumablybecauseofkineticef-fectsassociatedwiththelimitedheat-treatmenttimeofdenseceramicsfor6hinaninertatmosphereasopposedtoasmallamountofcrushedpowderinareducingatmosphere.Never-theless,theresultsfortheN2heat-treatedCCTOceramicscan

Fig.6.X-raydiffractiondataoftheceramicsurfacefora3hsampleafterheattreatmentat10001CinN2(bottomtrace)andthen,sequenti-ally,fromlayer-by-layerpolishedpelletsurfaces(upper

traces).

Fig.7.X-raydiffractionpatternofphaseassemblagefollowingTGAofCaCu3Ti4O12powderheatedto11001Cina5%H2

atmosphere.

Fig.8.SchematicillustrationofdecompositionreactionsoccurringinCaCu3Ti4O12ceramicsheattreatedat10001CinN2.

besummarizedschematicallyinFig.8.Attheinterfaceofthebulkphaseandthedecompositionzone,CaCuaphasemixtureofCaTiO3Tiposesinto4O12decom-discussionissimpli edtoexcludeoxygen3,Cu2O,andTiOlossfromthe2(thisbulkphaseand/orsecondaryphasesandthepresenceofSiOreactionproducts,2con-tamination).TheinnerlayercontainstheinwhichCaTiO3andTiO2coexistasamatrixstructureandCuwithinthatmatrix.Attheinterfacebetweenthe2Oasaprecipitateouterandinnerlayersofthedecomposition,volatilizationofCu2Ooccurs,leavingtheCaTiOouterlayer.Asstated3–TiO2matrixtoformapo-rous,‘‘coral-like’’previously,theelectricalpropertiesofthepolishedCCTOceramicsafterremovalofthesurfacelayersshowedthebulkresistivitytobeunalteredbytheheattreatmentinNdecreased2at10001C;however,thegrainboundaryresistivitybythreetofourordersofmagnitude.9Thisresultindicatesthatthecompositionofthegrainboundaryre-gionsinCCTOchangessignificantlyduringheattreatmentandpresumably,decompositioncommencesalongthegrainbound-ariesinCCTOceramicswheremassdiffusionofprimarilyCuandOissignificantlyhigherthanthatoccurringwithinthegrains.ThelackofvariationinbulkresistivityforsamplesheattreatedinNisunlikely2orOtobe2suggeststhattheoxygen-lossmodel(model2)theprimarysourceofsemiconductivityinCCTOceramics.

Suchlarge-scaledecompositionwasnotobservedinas-sinte-redsamples,althoughisolatedprecipitatesofCu2OandCaT-iSiO5wereobservedinsamplessinteredinairat11151Cfor24h.Inaddition,XRDofpelletsurfacesindicatethepossiblepresenceofCu‘‘Cu-rich’’grain2O,andotherworkershavereportedthepresenceofboundaries11

inCCTOceramicssinteredatelevatedtemperatures.IV.Conclusions

Theresultspresentedheresuggestthatlimitedreductionanddecompositionprocessesmayplayacentralroleinthedevel-opmentoftheelectricalmicrostructuresobservedforCCTOceramicssinteredinairat410501C.Furtherinvestigationsus-inganalyticaltransmissionelectronmicroscopyareinprogresstoprobenanoscalecompositionalvariationsinthegrain

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grainboundaryregionsofCCTOceramics.Thisshouldprovidemoreinformationregardingthecomposition–electricalpropertyrelationshipsinCCTOceramics.

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