Using crystallographic orientation mapping to examine stress concentrations and local crystallography in piezoelectric materials

铁电材料，如锆钛酸铅，由小的磁区组成，每个磁区具有沿不同方向的晶体单位晶胞的电极化及其相关的失真。这些领域如何相遇控制着宏观的、技术上重要的特性。尽管它们具有重要的商业价值，但关于这种材料中的局部结晶学以及它如何影响宏观性质，仍有许多未知之处。本申请人最近的研究还揭示了这种材料中多域结周围存在巨大的内应力，峰值超过1 GPa.很明显，这种高的应力集中将对材料的压电性能以及通过微裂纹进行疲劳的敏感性产生重大影响。确定局部结晶学和应力集中的理想方法是使用来自透射电子显微镜的菊池衍射图的自动索引来生成晶体取向图。由于瞬变电磁控制软件的计算机化，以及菊池图案自动索引软件的开发，这种方法最近变得可用。来自最终取向图的丰富信息将用于确定局部晶体参数，包括晶胞变形和多相组成中的物相识别，以及对微观结构中特定点处的应力集中进行量化。随后将与材料制造商讨论所得到的数据，以便了解局部晶体结构和局部应力集中如何影响材料的压电性及其在延长机电循环时的机械疲劳行为。

Ferroelectric materials such as lead zirconate titanate consist of small domains, each having the electrical polarisation and its associated distortion of the crystallographic unit cell along a different direction. How these domains meet up controls the macroscopic, technologically important properties. Despite their commercial importance, there remains much that is not known about this local crystallography in such materials and how it affects the macroscopic properties. Recent studies by the present applicant have also revealed the presence of large internal stresses around multidomain junctions in such materials, peaking at over 1GPa, and it is clear that such high stress concentrations will have a significant influence on both the piezoelectric properties, as well as the susceptibility to fatigue of a material via microcracking. The ideal method for the determination of the local crystallography and stress concentrations is the generation of crystallographic orientation maps using the automated indexing of Kikuchi diffraction patterns from the transmission electron microscope. Such a methodology has recently become available due to the computerisation of TEM control software, and the development of software for the automatic indexing of Kikuchi patterns. The wealth of information from the resulting orientation maps will be used to determine local crystallographic parameters including unit cell distortion and for phase identification in multiphase compositions, as well as the quantification of stress concentrations at specific points in the microstructure. The resulting data will then be discussed with the materials manufacturers in order to understand how the local crystallography and local stress concentrations are affecting the piezoelectric properties of materials and their mechanical fatigue behaviour on extended electromechanical cycling.