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钙钛矿氧化物薄膜在动态随机存储器、光电子器件和非挥发存储器等领域具有广阔的应用前景，是目前国际上倍受关注的功能材料。本文以典型的钙钛矿铁电体BaTiO3和PbTiO3为例，运用修正的Landau-Devonshire理论，研究铁电薄膜内的应力分布、相变行为、介电性质、畴结构，取得了以下有意义的结果：
(1)考虑膜与衬底的界面是非公度的情况，把生长于衬底上的外延铁电膜简化为理想的二维系统。假设在界面处膜与衬底的应变很小，通过推广Frenkel-Kontorova模型得到膜在界面上的剪应力。求解以此剪应力和弹性力学方程构成的边值问题，得到膜中应力分布的解析表达。该应力具有连续变化、张应力和压应力共存的特点。应力分布在边界处变化剧烈，在中心处基本均匀。厚膜中的应力集中于边界附近的小区域，在膜中心几乎为零。平均应力随膜厚增加而减少。
(2)忽略畴壁能和衬底中的弹性能对总能的贡献，运用修正的Landau-Devonshire理论并考虑膜中应力分布，我们发展了一套简洁的理论讨论膜的相变和介电性质。结果表明在低温铁电态，张应力有利于形成a-相，压应力有利于形成c-相。连续变化的应力导致相变弥散和介电反常。随着温度T升高并超过块体材料相变温度Tc，从应力绝对值小的地方到应力绝对值大的地方(相变温度Tcmax)连续出现一级相变。整个膜的平均效应，使得等效介电常数随温度的变化曲线ε33(T)连续光滑。随着膜厚或粒度的增加，ε33(T)的峰值温度Tm降低并趋于块体相变温度。应力幅值的增加导致ε33(T)峰值的降低。粒度或膜厚很小时a-相的介电峰消失。在室温下，介电常数随应力绝对值增加和膜厚的减小而减小。
(3)由于应力的影响，极化和介电常数分布不均匀：界面处的极化总是比膜中心的极化强，形成所谓的“超极化”；当T＜Tcmax，介电常数在界面处较小，Ⅱ可能形成“dead-1ayer”；对于c-相，当Tcmax＞T＞Tc时，膜内存在一个介电常数极高的薄层。在低温铁电态，膜中可能是a-相和c-相共存的。对于应变c/a较大的PbTiO3膜，其畴结构取决于膜与衬底在界面上晶格常数的匹配：晶格常数匹配良好时，膜中a-畴或c-畴占绝对优势；否则呈现a/c/a/c的交替畴结构。畴的稳定构型力图使膜与衬底的总应变最小。理论与实验吻合很好。
Perovskiteoxidefilmshaverecentlyreceivedconsiderableattentionduetotheirapplicationsinthedynamicrandomaccessmemory,optoelectronicdevices,andnonvolatilememories.Inthisdissertation,westudiedbytheextendedLandau-Devonshiretheorythestressdistribution,phasetransitionbehaviors,dielectricpropertiesanddomainstructureinBaTiO3andPbTiO3films.Themainworkandresultsareasfollows:Underconsideringthattheinterfacebetweenthefilmandsubstrateisincommensurate,theepitaxialfilmsonthesubstrateconstituteanidealtwo-dimensionalsystem,weemployanextendedFrenkel-Kontorovamodeltoobtaintangentstressontheboundaryofthefilmsbyassumingsmallstrainneartheinterfacebetweenthefilmandsubstrate.Theanalyticalexpressiononthestressdistributioninthefilmsisobtainedbysolvingtheelasticmechanicsequations.Thestresseschangecontinuously,fiatinthecenterandsharpnessintheinterface.Forthickfilm,thestressconcentratestoasmallregionclosetotheinterface,andbecomeszeroatthefilmcenter.Theaveragedstressreduceswithincreasingthefilmthickness.(2)Neglectingthecontributiontothetotalenergyfromtheself-energiesofdomainwallsandtheelasticfieldinthesubstrate,wedevelopaconcisephenomenologicaltheorytoinvestigatephasetransitionsanddielectricpropertiesintheferroelectricfilms.Thecalculatedresultsshowthatatlow-temperatureferroelectricstate,thecompressivestressisinfavorofformingc-phaseandthetensilestressinfavorofforminga-phase.Thecontinualstressesresultindiffusephasetransitionanddielectricanomaly.Whenthetemperaturegoesup,higherthanthatforthebulk,thefirst-orderphasetransitiontakesplacecontinuallyfromthesmallestabsolutevalueofⅢstressσ1tomaximum｜σ1｜.Theaveragedeffectmakesdielectricconstantε33(T)changecontinuallyandsmoothly.Thecurveoftheeffectivedielectricconstantonthetemperature,ε33(T),iscontinualandsmooth.Withincreasingthefilmthicknessorthegrainsize,thetemperatureatmaximumε33(T)decreasesandapproachesTcforthebulk.Withincreasingthestress,ε33(T)decreases.Fora-phase,thedielectricpeakdisappearswithdecreasingthefilmthicknessorthegrainsize.Thedielectricconstantdecreasesas｜σ1｜increasesorthefilmthicknessdecreases.(3)Thestresscausestheunevenpolarization.Thespontaneouspolarizationneartheinterfaceislargerthanthatatthefilmcenter,whichiscalledas‘super-polarization’.WhenT＜Tcmax,thedielectricconstantneartheinterfaceissmallerthanthatatthefilmcenter,formingso-called"deadlayer".WhenTcmax＞T＞Tc,agiantdielectricconstantlayerexistsinc-phaseinthefilm.Auniquemisfitstrain-accommodatingmechanismisproposedforPbTiO3filmsthatthephasetransitionattemptstominimizethemisfitstrainattheinterface.Whenboththefilmandsubstrateiswellmatched,purea-phaseorc-phaseappearsinthefilm,otherwise,alternativephasestructureofa/c/a/chappens.