Quantitative microstructural and spectroscopic investigation of inversion domain boundaries in sintered zinc oxide ceramics doped with iron oxide

It is known that sintering of powders of zinc oxide (ZnO) with small additions of iron oxide results in a ceramic with grains exhibiting a characteristic inversion domain micro-structure with planar inversion domain boundaries (IDBs) on two different habit planes. This study concentrates on a quantitative analysis, by a combination of different transmission electron microscopy methods, of those IDBs that are parallel to {0001} basal planes of the wurtzite structure of ZnO. Electron diffraction and dark-field imaging prove the nature of the inversion. High-resolution annular dark field scanning transmission electron microscopy allows measurement of the rigid body displacements across these IDBs and of the local lattice contraction related to the octahedral interstices that form the boundaries. Energy-selected imaging, electron energy-loss spectroscopy and energy-dispersive X-ray spectroscopy have been combined to determine the chemical composition of the IDBs quantitatively. It is thus shown unambiguously that every such fault consists of precisely one basal plane of octahedral interstices that are completely occupied by Fe3+ ions and that these FeO6 octahedra are themselves contracted along the <0001> direction. A local charge balance model explains the observations.