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1、10DiffusioninSomePerovskites:HTSCCupratesandaPiezoelectricCeramicDevendraGuptaIBMT.J.WatsonResearchCenter,YorktownHeights,NewYork10.1IntroductionUnderstandingofdiffusionprocessesinperovskites,representedbythehigh-temperaturesuperconducting(HTSC)cupratesandap
2、iezoelectricceramic,ofalltheconstituentelementsaswellasofsomeforeignatomicspecies,isimportantforscientificaswellastech•nologicalreasons.Self-diffusionofvariouscationsandanionspeciesinthesecompoundsisabasicmaterialproperty;ithasanimpactonthesuperconductingpro
3、pertiesoftheformerandthephysicalresponseofthelattertoelectrical,mechanical,andthermalfields.Theinterplayofdiffusionwiththemicrostructuresultimatelycontrolsthereliabilityofthedevicesinactualapplications.Onegoodexampleisthecontroloftwin-densityandgrainrefineme
4、ntsaccomplishedrecentlythroughcationdoping,whichinsomecasesalleviatestheflux-pinningprob•leminthematrix.[1]Therearemanysituationsinwhichcationdiffu•sionmanifestsitselfinthefabricationofHTSCelements.Inthebulkproductionoftapesandwiresproducedbytheoxide-powder-
5、in-tube(OPIT)method,forexample,silversheathistypicallyusedandthecompositeissubjectedtoseverethermomechanicaldeformation.[2]Insuchafabricationprocess,silversheathmaypartiallydissolveinthefabricationprocessandreachtheoxidecorebydiffusion,therebyreducingthecurr
6、ent-carryingcapacityoftheconnectors.Similarly,contactstotheHTSCandpiezoelectricthin-filmmicroelectronicdevicesinvolvemetallicelectrodesthattypicallyconsistofAgPdalloys.Acontrolledamountofdiffusionwouldpromoteadhesionandstrengthbetweenthefilmandthesubstratein
7、thefabricationprocesses.However,largeanduncontrolleddiffusionmaydegradethecriticalsuperconductingtemperature(Tc)'thecriticalcurrent(L),andotherphysicalcharacteristics,ashasbeenshowninthesubstitutionstudiesofseveralmetals,[3]andmayalsoleadtodevicedegradationd
8、uetomaterialreactions.Similarly,degradationofthedielectriccon•stantsandCurietemperaturemaybeexpectedinthepiezoelectric490DIFFUSIONPROCESSESINADVANCEDTECHNOLOGICALMATERIALSceramics,whichconsistof
