【作者】 王吉宁；

【导师】 费维栋；

【作者基本信息】 哈尔滨工业大学 ， 材料物理与化学， 2011， 博士

【摘要】 ABO₃型钙钛矿氧化物是具有许多突出物理性能的重要的功能材料体系,其在信息存储技术、多态记忆原件、变频器、传感器、卫星通讯、滤光器、促动器和微机电系统中均具有重要的潜在应用价值。Pb(Zr_1-xTi_x)O₃是ABO₃型钙钛矿氧化物家族的典型代表,由于其表现出优越的压电性能、铁电性能、介电性能及热释电性能,因而已为国内外学者广泛研究。但是其相图中准同型相界近邻区域内真实相组成仍然没有被确切证实,尤其是单斜相的存在区间依旧存在极大争议及相互矛盾的结果,且同一成份Pb(Zr_1-xTi_x)O₃单斜相的晶格常数相当分散,因而研究Pb(Zr_1-xTi_x)O₃相图中准同型相界近邻区域内单斜相的存在范围及单斜相的的晶格常数对于Pb(Zr_1-xTi_x)O₃相变行为的清楚理解及电学性能的优化具有重要的指导意义。残余应力及织构是薄膜的内在属性,其对铁电薄膜相变行为及晶格常数均具有重要影响,因而薄膜材料为Pb(Zr_1-xTi_x)O₃准同型相变的研究提供了一个良好的平台。本文通过溶胶-凝胶工艺制备了准同型相界近邻区域内不同成份的Pb(Zr_1-xTi_x)O₃薄膜,通过改变薄膜厚度来改变薄膜的残余应力,借助X射线ω扫描及ψ扫描技术表征薄膜的织构及残余应力,提出了一种基于X射线ψ扫描技术分析带有织构的薄膜相组成的方法,并系统的研究薄膜织构及残余应力对Pb(Zr_1-xTi_x)O₃薄膜相变行为的影响规律。通过实验研究发现,经过500oC预烧并650oC晶化处理的薄膜均具有（100）及（111）混合织构,（100）取向晶粒的残余应力状态为残余拉应力,而（111）取向晶粒的残余应力状态为残余压应力,这是由薄膜与衬底之间的晶格错配及不同取向晶粒间残余应力平衡作用共同导致的。通过对薄膜相变行为的研究发现,Pb(Zr_1-xTi_x)O₃薄膜中不同取向晶粒的相组成存在明显差异。Pb(Zr_0.58Ti_0.42)O₃、Pb(Zr_0.55Ti_0.45)O₃及Pb(Zr_0.54Ti_0.46)O₃薄膜中（100）取向晶粒的相组成为MA相,（111）取向晶粒的相组成为MB相,且随着薄膜厚度增加即残余应力的减小,MA相与MB相赝立方晶格a/c逐渐趋于1。对于Pb(Zr_0.52Ti_0.48)O₃薄膜及Pb(Zr_0.51Ti_0.49)O₃薄膜,当薄膜厚度小于200nm时,（100）取向晶粒的相组成为MA相,当薄膜厚度大于200nm时,（100）取向晶粒的相组成为MA相和四方相的混合相,且随着薄膜厚度的增加,MA→四方相相变量逐渐增加;（111）取向晶粒的相组成均为MB相和菱方相的混合相,且随着薄膜厚度增加,MB相→菱方相相变量逐渐增加;MA相与MB相赝立方晶格a/c随薄膜厚度增加逐渐趋于1。分析其原因,我们认为,（100）取向晶粒及（111）取向晶粒残余应力状态的不同导致了两种取向晶粒相组成的差异,且薄膜厚度增加导致的残余应力减小诱发了单斜相晶格常数比的变化。对单斜相而言,晶格常数比的变化意味着其自发极化方向的改变,这证明了单斜相自发极化方向对残余应力的敏感性。本文关于Pb(Zr_1-xTi_x)O₃薄膜相变行为的研究结果说明残余应力是导致单斜相晶格常数分散的重要原因。BiFeO₃是另一种典型的ABO₃型钙钛矿氧化物,其是唯一的在室温下具有铁电性及反铁磁性的单相多铁材料,并且BiFeO₃外延薄膜表现出巨大的自发极化及压电性能,但是BiFeO₃大的漏电流及高的结晶温度阻碍了其在功能器件中的应用。种子层能够有效的降低薄膜的漏电流及结晶温度,并能诱发薄膜织构,所以本文在不引入杂质的前提下在BiFeO₃薄膜与衬底之间制备Bi₂O₃种子层。通过研究发现,（111）Pt/Ti/SiO₂/Si衬底上无Bi₂O₃种子层的BiFeO₃薄膜没有织构,当晶化温度为650oC时,薄膜晶化不完全;带有Bi₂O₃种子层的BiFeO₃薄膜具有混合织构,且其在500oC下晶化良好;当外加100kV/cm电场时,Bi₂O₃种子层使BFO薄膜漏电流密度降低了两个数量级。上述结果说明Bi₂O₃种子层能诱发BiFeO₃薄膜混合织构的形成,并能有效的降低BiFeO₃薄膜的晶化温度及漏电流,这是由于,Bi₂O₃种子层能够为BiFeO₃提供了更多的形核质点,进而降低了BiFeO₃薄膜的结晶温度,此外,Bi₂O₃种子层在BiFeO₃薄膜与衬底之间起到了界面阻挡层的作用,降低了薄膜的漏电流,从而提高了薄膜的介电性能。更多还原

【Abstract】 ABO₃ type perovskite oxides exhibit many excellent physical properties, such as ferroelectric property, dielectric property, electro-optical effect, pyroelectric property, giant pizeoelectric property and magnetoelectric coupling effect. These excellent properties are essential to its potential application in actuators, sensors, and micro-electromechanical systems （MEMS）.Pb(Zr_1-xTi_x)O₃ is a typical material of ABO₃ type perovskite oxides. Due to its outstanding pizeoelectric property, pyroelectric property and ferroelectric property, it has been widely studied for many years. But there are still some ambiguous problems about its phase diagram and phase structure. The most important one is that the real phase structure of PZT in the vicinity of morphotropic phase boundary （MPB） is still in controversy. In addition, the lattice constants of monoclinic phase （M phase） quite differ in the various literatures. Therefore, clearly demonstrating M phase existence region and dispersion of M phase lattice constant possess a guidance significance for better understanding of PZT phase transition behavior. Residual stress and texture, which are intrinsic properties of thin film material, can greatly affect PZT phase transition behavior and lattice constants. In view of this, thin film material provides a platform for PZT phase transition research.In this dissertation, PZT thin films with the composition nearby MPB have been prepared by sol-gel technology. The residual stress is changed via adjusting film thickness. XRDω-scan andψ-scan are emploied to characterize the texture and residual stress. Based on XRDψ-scan technology, a method is built to characterize the phase compositon of thin film with texture. The dependence of PZT phase transition on the texture and residual stress of thin film is studied in detail. The results show that PZT films with different composition entirely exhibit mixed textures of （100） and （111）. Furthermore, the residual stress of （111）-oriented grains is compressive resulting from the lattice mismatch between PZT thin films and Pt substrate, and the residual stress of （100）-oriented grains is tensile due to the stress balance among different oriented grains. The research of phase transition of PZT thin films reveals the phase composition discrepancy of different oriented grains. For Pb（Zr0.58Ti0.42）O₃, Pb(Zr_0.55Ti_0.45)O₃ and Pb(Zr_0.54Ti_0.46)O₃ thin films, the phase composition of （100）-oriented grains is MA phase, and that of （111）-oriented grains is MB phase. As the film thickens, the M phase lattice constant ratio of c/a in pseudo cubic approaches 1 gradually, indicating the spontaneous polarization rotation of M phase. For Pb(Zr_0.52Ti_0.48)O₃ and Pb(Zr_0.51Ti_0.49)O₃ thin films with the thickness less than 200nm, the phase composition of （100）-oriented grains is MA phase. However, when the film thickness is more than 200nm, the phase composition of （100）-oriented grains is combined with MA phase and tetragonal phase （T phase）, and the content of T phase increases gradually as the film thickens. The phase composition of （111）-oriented grains is the mixture of MB phase and rhombohedral phase （R phase）. Moreover, the content of R phase increases gradually as the film thickens. The difference of phase composition between （100）- and （111）-oriented grains can be attributed to the different state of residual stress in different oriented grains. As the film thickens, the residual stress decreases, leading to the spontaneous polarization rotation of M phase, illustrating that the lattice constants of M phase is very sensitive to the variation of residual stress.BiFeO₃ （BFO）, another typical material of ABO₃ type perovskite family, is the only multiferroic material with ferroelectric property and antiferromagnetic property at room temperature. In addition, it had been reported that epitaxial BFO thin film possesses giant spontaneous polarization and piezoelectric property. Unfortunately, the high crystallization temperature and large leakage current restrict its application in the field of function device. Seed layer is a very effective route to decrease the crystallization temperature and leakage current, and can also induce the formation of the film texture. In this dissertation, Bi₂O₃ as the seed layer was prepared through sol-gel technology. The results show that the BFO thin film without seed layer fails to be crystallized well even at the high annealing temperature of 650oC and exhibites no texture, but the BFO thin film with seed layer can be crystallized well at such a low temperature of 500oC and exhibites the mixed textures.When the external electric field is of 100kV/cm, the leakage current of BFO thin film falls by two orders of magnitude because of the presence of the Bi₂O₃ seed layer. Taking the above results into consideration, the Bi₂O₃ seed layer can induce the formation of film texture. Moreover, it can effectively decrease the crystallization temperature and leakage current of BFO thin film.The detailed explanation is as follows. The Bi₂O₃ seed layer can provide much more nucleation sites for BFO thin film at lower temperature. Therefore, the BFO thin film can be crystallized at relative low temperature. In addition, the Bi₂O₃ seed layer forms an interface layer between thin film and substrate. In this case, the seed layer decreases the leakage current and enhances the dielectric property of BFO thin film.更多还原