Metastable ZrO2 crystal structures in electron beam evaporated thin films

Abstract

Electron diffraction evidence for the existence of metastable ZrO2 in thin zirconia films grown by electron beam evaporation is presented. X-ray powder diffraction results show that the films are at the boundary of the amorphous/crystalline state of the matter. Micro-regions of unknown crystalline structures of ZrO2 are formed during the growth and are observed by transmission and reflection electron diffraction. Two CaF2-type zircon oxides exist inside the films. They are the known high temperature cubic phase with lattice parameter a = 5.09 ± 0.08 Å and an isostructural analogue with a = 5.40 ± 0.10 Å. Series of hexagonal and cubic close packed structures, believed to be related to the packing of clusters, are also detected. The existence of metastable zirconia structures is explained by Ostwald's rule of stages. A comparison of some of the metastable oxide structures of ZrO2 films with their isostructural analogues observed in SiO2 and SnO2 films is included.