【word】 乌青铜型BaNd2Ti4O12微波介质陶瓷的电导和介电损耗

【word】 乌青铜型BaNd2Ti4O12微波介质陶瓷的电导和介电损耗 乌青铜型BaNd2Ti4O12微波介质陶瓷的电 导和介电损耗 August 物理化学学~(WuliHuaxueXuebao1 ActaP.一Chim.Sin.2011,27(8),2009-20142009 [Article]www.whxb.pku.edu.ca 乌青铜型BaNd2Ti40,2微波介质陶瓷的电导和介电损耗 夏海廷匡小军.,’王春海’李文先荆西平’赵飞岳振星 (北京大学化学与分子工程学院,北京分子科学国家实验室,稀土材料化学及应用国家重点实验室,北京100871;内蒙古大 学化学与化学工程学院,呼和浩特010021;.中山大学化学与化学工程学院,教育部生物无机与合成化学重点实验室,光电材 料与技术国家重点实验室,广州510275;清华大学材料科学与工程系,新型陶瓷和精细工艺国家重点实验室,北京100084) 摘要:用固相反应合成了乌青铜型钛酸盐陶瓷BaNdTi0并用电化学阻抗和微波介质谐振测试表征了不同 热处理和钽掺杂对电导和微波介电损耗的影响.电导率随退火气氛(空气,氧气和氮气)的变化与缺陷反应平衡 20一2V.+OT+2e和T+e一T随氧分压的变化一致,表明BaNdTiO具有n型导电性质.在空气和氧气 中退火有利于减少包括V,T和弱束缚电子在内的本征缺陷因而降低 电导.而在低氧分压的氮气中进行退火 处理,增加了缺陷的浓度,同时提高了电导率.在空气/氧气,氮气中的 退火处理对微波介电损耗没有明显的影 响,表明本征缺陷对微波介电损耗的影响可以忽略.空气退火处理样 品的电导率和微波介电损耗低于空气淬火 处理的样品:其中电导的变化与缺陷反应平衡相关,但空气退火降低 微波介电损耗可能与退火消除晶格热应力 有关.五价钽的掺杂降低了电导但增大了微波介电损耗.本研究表明 空气退火处理能有效地改善BaNd:TiO 陶瓷的品质因子Q×其值提高了约12%. 关键词:缺陷;电导:微波介电损耗:BaNdTi0:乌青铜结构 中图分类号:0646 ConductivityandDielectricLossofTungsten--Bronze-TypeBaNd=Ti,012 MicrowaveCeramics XIAHal—TingKUANGXiao-Jun.,\/,fANGChun—Hai’LIWell—XJan JlNGXi—PingZHAOFeiYUEZhen.Xing rBeringNatiohalLaboratoryforMolecularSciences,StateKeyLaboratoryofRareEarthMaterialsChemistryandApplications CollegeofChemistryandMolecularEngineering,PekingUniversity,Beijing100871,PR.China;CollegeofChem&tryand ChemicalEngineering,InnerMongoliaUniversity,Hohhot010021,PR.Chi na;MOEKeyLaboratoryofBioinorganicand SyntheticChemistry,StateKeyLaboratoryofOptoelectronicMateriaIsandTechnologies,SchoolofChemistryandChemical Engineering,SunYat-SenUniversity,Guangzhou510275.PR.China;4StateKeyLaboratoryofNewCeramicsandFine Processing,DepartmentofMaterialsScienceandEngineering,TsinghuaUniversitY,Beijing100084,PR.Chin Abstract:Tungsten—bronzetypetitanateBaNd2Ti4O12ceramicsweresynthesizedbysolidstatereactions. TheconductivityandmicrowavedielectriclOSSofthesamplesthatwerethermallytreatedundervarious conditionsandTa—dopedwereinvestigatedbyelectrochemicaIimpedancemeasurementandmicrowave dielectricresonatormeasurement.Thevariationinconductivitywithannealingatmospheresofair,O2,and N2wasconsistentwiththedeflectequilibriums20H2V.+O2T+2eandT+eHTi,suggestingntype conductanceforBaNd2Ti4O12_Thermaltreatmentinair/O2WaSfoundtofavortheeliminationoflhenative defectsV,mitTiandweaklyboundelectronsthusdecreasingtheconductivity.ThermaltreatmentinaN, atmosphere,whichhadaIowoxygenpartialpressure.increasedthedefectcon tenlandtheconductivity~ Thermaltreatmentinair/O2/N2didnotclearlyaffectthemicrowavedielectricloss,suggestingthatnative Received:April29,2011;Revised:June12,2011;PublishedonWeb:June28.2011. Correspondingauthors.KUANGXiao—Jun,Email:kuangxj@mail.sysu.e du.cn.JINGXi-Ping,Email:xpjing@pku.edu.Cr1. TheprojeetwassupportedbytheNationalNaturalScienceFoundationofChina(20821091,21071009,20423005). 国家自然科学基金(20821091,21071009,20423005)~助项目 ?EditorialofficeofActaPhysico—ChimieaSinica 2010ActaPhys.一Chim.Sin.2011Vo1.27 defectshavenegligibleeffectsonthisprope~y.Theair.annealedsamplewasfoundtohavelower conductivityandIowermicrowaveIosscomparedwiththeair—quenchedsa mple.Thechangein conductivitywasfoundtoberelatedtotheequilibriumofthenativedefectsbutthechangeinmicrowave dielectricIossmightbeexplainedbythereleaseofthermallyinducedIatticestrain.Tadopingreducedthe conductivitybutincreasedthemicrowavedielectricIoss.Thisworkshowsthatair—annealingmaybean efficientwaytoimprovetheQxffactorforBaNd2Ti4O12ceramics,whichwasenhancedbv,12%. KeyWords:Defect;Conductivity;Microwavedielectricloss;BaNd2Ti4012;Tungsten—bronze 1Introduction Theminiaturizationofmicrowavetelecommunicationcom— ponentssuchasresonatorsandfiltersrequiresdielectricmate— rialswithhighdielectricpermittivity(0,lowdielectricloss stable (tan5)orhighqualityfactor(Q=1/tanfi)andtemperature— resonancefrequency(taatmicrowavefrequency..Thesethree keyparametersarealmostalwaysmutuallyexclusiveindielec— tricmaterials,whichcomplicatetheoptimizationofmicro— wavedielectricpropertiesfordevelopingnewmicrowavedi— electrics.Amongthesethreeparameters,dielectriclosscom— prisesintrinsiclossfromvibrationanharmonicityofperfectlat— riceinmaterialsandextrinsiclossinducedbyprocessing,such asporosity,defects,impurities,grainsizeetc.Optimizationof qualityfactorusuallyreferstominimizationofextrinsicloss, whichisstillachallengeduetolackofclearunderstandingon thefundamentalphysicsofmicrowavedielectriclossandthe underlyingchemistryonthecomposition,structure,andde— fects. Thereareconsiderableinterestsontitanate—basedmicro. wavedielectricceramics,suchasa—PbO2一typeZrl一SnTi04, bariumpolytitanatesBa2Ti9O20/BaTi4O9,tungsten—bronze—type Ba6-3xR8+2xTil8O54(Risrareearthelements),ilmenite—perovskite compositeMgTiO3?CaTiO3,perovskite—typeLaAl03一CaTiO3, andB—sitedeficienthexagonalperovskitestitanateBaLa4Ti4O becauseoftheirexcellentmicrowavedielectricproperties.In thetitanate.baseddielectricceramics,theoccurrenceofoxy— genlossandTipartialreductionarecommonduringthehigh temperaturesinteringprocess,whichhindertheoptimizationof theirQfactors.’Thustheprocessingoffiringtheceramics intheatmospherewithhighoxygenpartialpressureanddoping toeliminateoxygenlossandreductionofTiwereemployed toimprovetheQfactorsofthetitanate-baseddielectricceram— ics,whichwerehighlightedinthepreviouspublications.,’ Forunderstandingthecorrelationbetweenthedefectsassociat— edwiththeoxygenloss(V~)/titaniumpartialreduction(Tin) andthemicrowavedielectriclOSSintitanate—baseddielectrics. MgTiO3ceramicwaschosenasamode1materia1fortitanatedi— electricsanddielectriclOSSspectrumofthismateria1wasinves- tigatedoverawidefrequencyrangeinourpreviouswork.We proposedthatlowfrequencyconductionarisingfromelectron hoppingandrelaxationofatomicdefectpolarizationcontrib— uteslittletothemicrowavedielectric1OSSandtheatomicde— fectsmayaffectthemicrowavedielectriclossviamodifying theanharmonicityoflatticevibration.Ourrecentworkson MgTi0ceramicsandCaTiOceramicsindicatedthatnative defects,suchasV0xandTiH,andweaklyboundelectrons,only affectedthelowfrequencyconduction,butnotthemicrowave dielectriclOSS. baseddielectrics,tungsten-bronzetype Amongthetitanate— Ba6一hR8+2xTi18O54(R=La,Pr,Nd,Sm,Eu,Gd)havereceivedmuch attentionbecauseoftheirhighpermittivityr.,70—150)and tunablechemicalcompositions.HighQfactorwasob tainedonNdandSmanaloguesatcompositionaroundx=2/3 duetotheA—cationordering’andzeronwasachievedby combiningNdanaloguewithpositiveandSmanaloguewith negativee.g.,Ba42Sm736Nd,84Tils0s,e-84,Q产9000GHz(厂’ isresonancefrequency).0×10’.C,.Thistungsten—bronze phasewasinitiallyreportedwithaformulaBand2Ti5Ol4byKo— lrdr口7.”instudyingtheternaryphasediagramofBaO— Nd2O3一TiO2anditscompositionwas1atercorrectedas BaNd2Ti4O12.Varfolomeeveta1.foundthatthiscompound formedsolidsolutionasBar一3xR8+2xTil8O54and0hsatoeta1.de— terminedthesolidsolutionlimitsforNdandSmanaloguesasO 0.7and0.3<J<0.7,respectively.IntheBa6_3.Nds~2xTi18054solid solution,thematerialBaNd2Ti4Ol2(=0.5)exhibitedgoodmi— crowavedielectricpropertyof,,85,Q5000—6000GHzex— ceptforitshight~100×10.C,.Inthisstudy,air-annealing/ air-quenching,thermaltreatmentsinvariousatmospheres(air, O2,andN2)aswellasTa—dopingwereconductedon BaNd2Ti4Ol2ceramics.Theinfluencesofthevarioustreatments ontheconductivityandthemicrowavedielectriclOSSofthe BaNd2Ti4012ceramicswereinvestigatedandthecorrelations amongthedefects.conductivity,andmicrowavedielectriclOSS aredjscussed. 2Experimental PolycrystallineBaN也Ti4O12ceramicsampleswereprepared usinghightemperaturesolidstatereactions.Stoichiometric amountsofBaCO.(AR),Nd2O(99.9%),andTiOz(AR)as startingmaterialswereweighedandmixedbyballmillingin ethano1withagateballsfor24h.Theethanolwasremovedby vacuumfiltrationandthemixedpowdersweredriedinair.The powderswerethencalcinedat1150.Cfor3h.Furtherthe powderswerere.ball—milledinethanolfor20h.Atierfiltration anddryingprocesses.afewdropsof3%aqueoussolutionof polyvinylalcohol(PVA)wasaddedintothedriedpowdersas No.8XIAHai—ringeta1.:ConductivityandDielectricLossofTtmgsten-Bronze—TypeBaNd2ThO12MicrowaveCeramics2011 binderandthepowderswerepressedintopelletsbyuniaxial pressing.Thepelletswerethenfiredat550.Cfor2htore— movethePbinder.followedbysinteringat1350oCfor4h inaiTwithaheatingrate20.C’min一.Aftersintering.thepellets werecooledspontaneouslyinthefurnace.1eadingtoas—sintered sample,BNT-O.Allthepelletshadrelativedensityof一96%, whichwascalculatedusingtheweightsanddimensionsofthe pelletsaswellastheX--raytheoreticaldensity.Fortheprepara-? tionofTa-dopedsamples,suitableamount(<2%,molarfrac- tion)ofTa20,(highpurity)wasaddedaccordingtothenominal compositionBaNd2Ti4Ol20handthecalciningandsinter. ingprocessesarethesalTleasthoseforBNT-0. Formodifyingthedefectcontents.varioustherma1treat- mentswereconductedontheBaNd2Ti4O12samples.Air.annea1. ingwasperformedonasinteredpellet,heatedat1100.Cfor4 hinairandthencooledto400.Cwitharateof2.C?min一in afurnacebeforebeingtakenouttocooldowntoambienttem— perature.resultinginsampleBNT_1.Theair-quenchingwas carriedoutbytakingoutasinteredpelletquicklyfromfurnace atll00.Cafterbeingheatedat1100.Cfor4hthencooling thepellettoambienttemperatureinair,producingsample BNT_2.Thethermaltreatmentsinair/O’2/N2atmosphereswere performedbyheatingthesinteredpelletsinatubefurnacewith air,O2,orN2atmosphereat650.Cfor4h.Afterthetreat— ments,thepelletsamplesweretakenoutfromthetubefurnace quickly,andthencooleddowntoambienttemperature,leading tosamplesBNT-3(air),BNT_4(O2),andBNT-5(). PhaseassemblageswerecheckedbypowderX..raydiffrac.. tion(XRD,RigakuD/max2000diffractometer,Japan;CuKa radiation,graphitemonochromator).Alltheceramicsamples studiedinthisworkhavepureorthorhombicphase,agreeing withJCPDSfile44-61.Electrochemicalimpedancespectra wererecordedinthefrequencyrangeof5Hz-13MHzusing animpedance/gain-phaseanalyzer(ModelHP4192A,USA), whichwasconductedatvarioustemperaturefrom200to800.C inairwithheatingandcoolingcycles.TheACimpedancemea— surementswerealsoconductedindifferentatmospheresat 650.CandtheatmospherewaschangedaccordingtothefoI— lowingsequence:air02__+N202.Thegasflowratewas keptat~500mL?min一andeachatmospherewasmaintained for5-10h.Priortothemeasurements,platinumpastewas coatedontwooppositesurfacesofthepelletsandfiredat800. Cfor10mintoburnofftheorganiccomponentstoformelec— trodes.Microwavemeasurementsinthefrequencyrangeof50 MHz-20GHzwereconductedusinganetworkanalyzer(HP 8720ES.USA).Thepermittivity8wasmeasuredusingthe HakkiandColemandielectricresonatormethodbyexciting theTE0llresonantmodeofthedielectricresonatorswhilethe unloadedOfactorwasmeasuredusingtheTEo15mode. 3Resultsanddiscussion 3.1Electrochemicalimpedancemeasurementsfor BaNd2Ti4012ceramics E p a 一 N Z/(kQcn1) Fig.1ElectrochemicalimpedanceplotofBaNd2Ti40nceramicat 700.CinairandanequivalentcircuitofparallelRbandfor modelingtheimpedancedata Atypicalcompleximpedanceplotlz一Zplot)of BaNd2Ti4OI2ceramics(BNT-O,measuredinairat700.C)is showninFig.1.inwhichasinglesemicirculararcisobserved. Anequivalentcircuitwithresistorb)andcapacitor(G)in paralle1isrequiredtomodelthissemicirculararc.Theassoci atedRbvaluecanbeestimatedastheinterceptofthesemicircu. 1ararcatlowfrequencyandthevaluecanbeestimatedfrom theequivalentcircuitfitting.Thevalueis,7pF?cm,,ap— proximatelyconsistentwiththepermittivitymeasuredatmicro wavefrequency=85)andindicativeofbulkresponseforthe semicirculararc.Nosignificantresponsesfromgrainboundary andelectrodeweredetectedoverthemeasuredfrequency rangeandtemperaturerange. Variationsofbulkconductivity(=I/Rb)ofBaNd2Ti4O12ce— ramie(BNT-0)withtemperaturesinaheatingandcoolingcy— clefrom420to700.CarerepresentedbyArrheniusplots (Fig.2).TheArrehniusplotofthebulkconductivityonheating showscurvaturearound460-500.Cwithactivationenergy C巴)transitionfrom0.30eVinlowtemperaturerange(420—460 .C)to0.76eVinhightemperaturerange(540—700.C).Below 540.C,theconductivityintheheatingprocessishigherthan thatinthecoolingprocessandconductivitiesinthebothheating andcoolingprocessesarealmostidentica1above540.C. Suchconductionbehaviorissimilartothoseobservedin someothertitanates,suchasBaEu2Ti4Ol2”andMgTiODe E a b 10.T一’/K一’ Fig.2ArrehniusplotsofthebulkconductivityofBaNd2TLOl2 cerumic 2012ActaPhys.一Chim.Sin.2011VO1.27 feetequilibriumsassociatedwithoxygenlossandTipartial reductionmaybeappliedforunderstandingthisphenomenon. Duringsinteringathightemperature,thedefectsaregenerated inBaNd2Ti4Ol2: 0—V1/20T(1) Vcancontributeweaklyboundelectronsandtheseelec— tronscanpartiallyreduceTitoTi”,i.e., V一V’+2e(21 Ti,+e一Ti(3) TheconductanceintheBaNd2Ti4Ol2ceramicisrelatedtothe contentoftheweaklyboundelectronsthatareassociatedtothe defectsofVoandTi(Ti”),correspondingto//-typeconduc— tion.NoresponseofionicconductionwasobservedintheAC impedancespectradescribedabove.Above540.C,Eaconsists oftwoterms:generationenergyofthedefects/electronsvia equilibration(1)andpotentialenergyforthetrappedelectrons hoppingover.Below460.C,thedefectsgeneratedinthesin— teringprocessatelevatedtemperaturearefrozenandEmay onlybeassociatedtothepotentialenergyforthetrappedelec— tronshoppingover.Therefore,Einthehightemperaturerange of540-700.Cappearshigherthanthatbelow460.C.Inthe heatingprocess,whenthetemperatureincreasedover460.C, thedefectequilibrationtakesplace,whichshiftstotheleftand reducesthedefectcontent.Thisaccountsforthegradualin— creaseoftheconductivityovertherangeof460-540.C.Above thisrangethedefectequilibrationreachesandtheconductivi— tiesinthebothheatingandcoolingprocessesdonotshowap— parentdifference.Inthecoolingprocessbelow540.C,thema— terialcontainslowercontentsofdefectsthanthatintheheating processduetoannealingeffectthusalowerconductivity印一 pears. Fig.3showstheconductivityvariationswithtimeinvarious atmospheresat650.Cinanin—situmeasurement.Theinitial measurementwasconductedinair,followedbyaswitchse— quence:O2—?N2—?O2.Whenthesamplewasinitiallyheatedin air,theconductivitydecreasedgradually.Aftertheatmosphere wasswitchedtoO2,theconductivitydecreasedcontinuously. WhiletheatmospherewasswitchedfromO2toN2,theconduc— tivityincreaseddramatically.Finally,whenwealteredtheat— mospherebackto02again,theconductivitydecreasedsharply andalmostapproachedtothelevelafterthefirst02heating. Theseresultssupportthattheequilibriums(1)to(3)occurred inBaNd2Ti4O12ceramics.Theinitialheatinginairreducedthe , E 9 a t,min t,rain Fig.3Bulkconductivityvariationswithtimeinvarious atmospheresinaswitchingsequenceofair_+02_?N2_?o2at650.C contentsoftheintrinsicdefects(e.g.Vandtheweaklybound electrons)arisingfromthehightemperaturesintering,i.e.,the equilibriums(1)to(3)shiftedtoleftduringtheheatingprocess inair.ThefollowingheatinginO2increasedthe02partialpres— sure,leadingtotheequilibriumsfurthershiftingtoleftandthe conductivitywasreduced.Theconductivityincreasedduring theheatingprocessinN2atmosphereduetoitslow02partial pressure,whichdrovetheequilibriumsshiftingtoright.The . typeconductionbehaviorofBaNd2Ti4Ol2ceramicwasfur— therconfirmedbythedatainFig.3. 3.2MicrowavepropertiesofBaNd2Ti4012ceramics Themicrowavedielectricpropertymeasurementswerecar— riedoutfortheBaNd2Ti4012ceramicsamples,whichhadbeen thermallytreatedinvariousconditions.Thepermittivitywasin— sensitivetothe