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

Selected area and Kikuchi diffraction patterns, traditional bright field and dark field imaging techniques in electron microscopy as well as high resolution TEM and STEM techniques, together with electron backscattered electron diffraction technique have been used to study the domain structures, local crystallography and atomic structures in PZT-based materials. Reliable EBSD mapping of 90° domains in a tetragonal Pb(Zrx; Ti1-x)O3 with x = 0.5 ferroelectric perovskite has been achieved for the first 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° 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 diffraction, 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 structure in La-doped zirconium-rich lead zirconate titanate have been revealed in detail for the first time. The structure is dominated by 60° domain boundaries close to {101} planes of the primitive perovskite cell; and tilts of the perovskite sublattice of about 0.5° 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 diffraction 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° domain boundaries are also observed but are less frequent than 60° boundaries and in contrast to previous reports, these often have rather curved and irregular boundary planes. The atomic arrangement of these 90° boundaries was studied by aberration corrected HRSTEM. Different stackings and periodicities were identified.