PLYSICALREVIE%'VOLUME1~9,NUMBER41SFEBRUARY1963TemyeratureDeyendenceofDielectricConstantsofCubicIonicComyoundsA.J.BoslKANAiNDE.E.HAvINGAI'hilipsResearchLaboratories,X.V.I'hilips'GloeilamPenfabriekenBindhoeen-Vetherlands(Received19September1962)Thetemperatureandpressuredependenceofthedielectricconstantofanumberofcubichalidesandoxideswithabroadrangeofdielectricconstantshavebeendetermined.Forlow-~compoundsthedielectricconstantincreaseswithincreasingtemperature,whereasforhigh-ecompoundsthedielectricconstantde-creaseswithincreasingtemperature.Hydrostaticpressurelowersthevalueofthedielectricconstantforallcompoundsmeasured.l.orferroelectricsandantiferroelectricsarelationhasbeenfoundbetweentheCurietemperatureandtheCurieconstant.Threeeffectscontributetothetemperaturedependenceofadielectricconstant:thedecreaseinthenumberofpolarizableparticlesperunitvolumeasthetemperatureincreases,whichisadirectresultofthevolumeexpansion(A),theincreaseofthemacroscopicpolarizabilityduetothevolumeexpansion(8),andthetemperaturedependenceofthemacroscopicpolarizabilityatcon-stantvolume(C).Theexperimentaldatahavebeenusedtocalculatethesedifferentcontributions.Itisfoundthatthevolume-dependentcontribution(A+8)isalwayspositiveandthatthedirecttemperaturecontribution(C)canbeeitherpositiveornegative.Whereopticaldatawereavailableinliteraturetheywereusedtocalculatethecontributionsoftheopticalandinfraredpartsofthepolarizabilitytothetemperatureandvolumedependenceofthepolarizability.Theresultsarediscussedwiththeuseofaclassicalionicmodel.I.INTRODUCTIONinAuencesaffectitsmagnitude.Itcan,namely,beshown'Napreviouspaper'ithasbeenshownthatthreethattheinternalQeldsduetothenon-cubicenviron--~effectscontributetothetemperaturedependenceofmentsmakethemselvesnoticeableonlyoverratherthedielectricconstanteofacubicorisotropicmaterial.shortdistances.Intheperovskitestructure,forexample,ForsuchamaterialthemacroscopicClausius-3Tossottithemaincontributiontothesefieldsarisesfromtheformula1)olds:nearestne