Materials World Network: Effects of Constraints and Thickness on Perovskite Ferroeoectrics Undergoing Tilt Transitions

这个宾夕法尼亚州立大学、阿贡国家实验室和谢菲尔德大学（英国）之间的合作项目旨在了解钙钛矿薄膜中的倾斜转变。 这些倾斜转变是由于氧八面体框架的协同运动而发生的，并且是钙钛矿结构化合物中最常见的相变。这种转变对谐振频率的温度系数和压电常数有深远的影响。 尽管它们的重要性，物理的尺寸效应和机械约束的效果（如在薄膜中），这些倾斜过渡的位移/有序过渡相比，知之甚少。在这个项目中，我们试图回答以下问题，这些问题将使我们对约束系统中倾斜转变的理解取得突破：1。弹性边界条件如何影响钙钛矿的倾斜转变？2.铁电体尺寸效应是否受倾斜转变的影响？3.倾斜畸变稳定性变化的性质后果是什么？PbZr 1-xTixO 3、AgTa 1-xNbxO 3和BiScO 3-PbTiO 3的外延薄膜将以在体中产生倾斜转变的组合物生长。相变序列作为膜厚度，面内横向约束，温度和组合物的函数将研究通过对铁电，介电和机电性能的影响，通过常规的X射线散射，并通过同步加速器X射线散射在先进的光子源（APS）。 与谢菲尔德大学的Ian Reaney教授一起，还将通过透射电子显微镜和拉曼散射来询问薄膜。

This collaborative program between Penn State University, Argonne National Laboratory and the University of Sheffield (UK) is directed towards understanding tilt transitions in perovskite thin films. These tilt transitions occur due to cooperative motions of the oxygen octahedra framework, and are the most common phase transitions in perovskite structured compounds. Such transitions have a profound impact on the temperature coefficient of resonance frequency and on piezoelectric constants. Despite their importance, the physics of size effects and the effect of mechanical constraint (as in thin films) for these tilt transitions is poorly understood in comparison to displacive/ordering transitions. In this program, we seek to answer the following questions that will allow breakthroughs in our understanding of tilt transitions in constrained systems:1. How do elastic boundary conditions affect the tilt transitions in perovskites?2. Are ferroelectric size effects affected by tilt transitions?3. What are the property consequences of changes in the stability of tilt distortions?Epitaxial thin films of PbZr1-xTixO3, AgTa1-xNbxO3 and BiScO3-PbTiO3 will be grown with compositions that yield tilt transitions in the bulk. The phase transition sequence as a function of film thickness, in-plane lateral constraint, temperature and composition will be studied via impact on ferroelectric, dielectric, and electromechanical properties, by conventional x-ray scattering, and by synchrotron x-ray scattering at the Advanced Photon Source (APS). In conjunction with Prof. Ian Reaney of the University of Sheffield, films will also be interrogated by transmission electron microscopy and Raman scattering.