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

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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.