Role of Interfacial Energy and Crystallographic Orientation on the Mechanism of the ZnO + Al2O3 → ZnAl2O4 Solid-State Reaction: II. Reactivity of Films Deposited onto the Sapphire (001) Face

The initial steps of the reaction between ZnO and (001)-oriented Al2O3 single crystals have been investigated with X-ray diffraction, atomic force microscopy, and X-ray absorption spectroscopy at the Zn-K edge starting from 45 nm thick zincite films. The reaction eventually yields the ZnAl2O4 spinel on this interface but via a complex mechanism involving side and intermediate nonequilibrium compounds, the spinel initially forming with a distribution of lattice parameters. Evidence is given of the fact that one of the side compounds has a crystal structure close to that of the Zn3In2O6 compound. The results are discussed in the general context of the same reaction on different single-crystal substrates and different film thicknesses.