New approach to the study of solid-state reactions in oxide ceramics

High-quality 100 nm thin films of NiO were grown on single-crystal (0001) α-Al2O3 substrates by pulsed-laser ablation. The resultant microstructure consists of two twin variants such that the (111) plane in both NiO twins is parallel to the basal (0001) plane of α-Al2O3. They differ by a rotation of 60 or 180° about the [0001] axis. Furthermore, the microstructure of those twins can be made to conform to the underlying substrate steps with the result being twin grains on the order of 200-400 nm wide and many tens of microns long. Scanning and transmission electron microscopy studies were performed to determine the mechanism and kinetics of the solid state reaction.