Decomposition reactions in CaCu3Ti4O12 ceramics(4)

2836JournaloftheAmericanCeramicSociety—Adamsetal.Vol.89,No.9

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

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