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

这项由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)合作的项目旨在了解钙钛矿薄膜的倾斜转变。这些倾斜转变是由于氧八面体骨架的协同运动而发生的，是钙钛矿型结构化合物中最常见的相变。这种转变对共振频率的温度系数和压电常数有很大的影响。尽管它们很重要，但与位移/有序转变相比，对于这些倾斜转变的尺寸效应和机械约束(如在薄膜中)的影响，人们了解得很少。在这个项目中，我们试图回答以下问题，以突破我们对受限系统中倾斜转变的理解：1.弹性边界条件如何影响钙钛矿中的倾斜转变？2.倾斜转变是否影响铁电尺寸效应？3.倾斜扭曲稳定性变化的性质后果是什么？PbZr1-xTixO_3，AgTa1-xNbxO_3和BiScO_3-PbTiO_3外延薄膜将在体相中生长产生倾斜转变的组份。相变序列将通过对铁电、介电和机电性能的影响、常规X射线散射和先进光子源(APS)的同步辐射X射线散射来研究，作为薄膜厚度、面内横向约束、温度和成分的函数。与谢菲尔德大学的Ian Reaney教授一起，还将对薄膜进行透射电子显微镜和拉曼散射测试。

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.