Microstructure, nanostructure, and local crystallography in perovskite ferroelectrics and antiferroelectrics

Abstract

Selected area and Kikuchi diraction patterns, traditional bright eld and dark eld imaging techniques in electron microscopy as well as high resolution TEM and STEM techniques, together with electron backscattered electron diraction technique have been used to study the domain structures, local crystallography and atomic structures in PZT-based materials. Reliable EBSD mapping of 90 degrees domains in a tetragonal Pb(Zrx; Ti1-x)O3 with x = 0.5 ferroelectric perovskite has been achieved for the rst time, together with reliable automated orientation determination from TEM-Kikuchi patterns. This has been used to assess the local crystallography of domains by determining misorientation angles at 90 degrees domain boundaries and thus local c/a ratios. In most cases, a good agreement is found between local c/a ratios and global measurements by X-ray diraction, but some clear discrepancies have also been found suggesting that real local variations are present, perhaps as a consequence of compositional inhomogeneities. The details of the domain structure of the incommensurate antiferroelectric struc- ture in La-doped zirconium-rich lead zirconate titanate have been revealed in detail for the rst time. The structure is dominated by 60 degrees domain boundaries close to {101} planes of the primitive perovskite cell; and tilts of the perovskite sublattice of about 0.5 degrees are also noted at such boundaries consistent with a small tetragonal distortion of the primitive cell. Within each domain a streaked nanostructure is revealed under weak diraction conditions perpendicular to the long b-axis of the incommensurate supercell, which appears to be a consequence of planar faulting perpendicular to this b-axis. 90 degrees domain boundaries are also observed but are less frequent than 60 degrees boundaries and in con- trast to previous reports, these often have rather curved and irregular boundary planes. The atomic arrangement of these 90 degrees boundaries was studied by aberration corrected HRSTEM. Dierent stackings and periodicities were identied