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1、4092Chem.Mater.2008,20,4092–4098StructuralDependenceofMicrowaveDielectricPropertiesofSrRAlO4(R)Sm,Nd,La)Ceramics:CrystalStructureRefinementandInfraredReflectivityStudyXieChengFan,XiangMingChen,*andXiaoQiangLiuDepartmentofMaterialsScience&Engineering,ZhejiangUniVersity,Hangzhou310027,ChinaRec
2、eiVedNoVember16,2007.ReVisedManuscriptReceiVedMarch27,2008ThecrystalstructurerefinementandinfraredreflectivitystudywerecarriedoutforSrRAlO4(R)Sm,Nd,La)ceramicswithK2NiF4structuretoinvestigatethecorrelationsbetweenthecrystalstructure,polar-phononmodeparameters,andmicrowavedielectricproperties
3、.Fouriertransforminfraredreflectivity-1spectraintherangeof50-4000cmweremeasuredandevaluatedbymeansofclassicaloscillatorfit.Thedatawereextrapolatedbelowthemeasuredfrequencyrangetoestimatetheintrinsicmicrowavelosses.Heavydistortionsof(Sr,R)O9dodecahedraandAlO6octahedraareobservedinthecrystalst
4、ructureandtheyshouldattributetointerlayerelectricpolarizationandinterlayersizemismatch.Thetwolowest-frequencypolar-phononmodes,whichgiveprimarycontributionstothemicrowavecomplexpermittivity,arethebendingandstretchingvibrationsof(Sr,R)-AlO6,sothatthedistortionof(Sr,R)O9dodecahedrahasagreati
5、mpactonthedispersionparametersofthesetwomodesandconsequentlyaffectspolarizabilitiesandintrinsicdielectriclossesofSrRAlO4greatly.TheabovefindingsprovidethegeneralguidelineformodifyingtheintrinsicmicrowavedielectricpropertiesforSrRAlO4ceramics.Moreover,thecalculatedQ×fvaluesare25000-85000GHzh
6、igherthanthemeasuredones,andthissuggeststhegreatopportunitytoimproveQ×fthroughoptimizingthemicrostructures.IntroductionSincethe1970s,dielectricmaterialshavebeendevelopedandputintopracticaluseforresonators,filtersandoscillatorsatmicrowavefrequencies.Thegrowthofthemobilephonemarketinthe1990sl
7、edtoextensiveresearchanddevelop-mentinthisarea.Tomeettheindustrialrequirements,currentdevelopmenttrendsofmicrowavedielectricceramicsare(1)reducingthecostbydevelopingnewmaterialswithoutnobleelementssuchasTaandNb,(2)reducingtheextrinsicdielectricloss,and(3)lower
