Metastable ZrO2 crystal structures in electron beam evaporated thin films

Electron diffraction evidence for the existence of metastable ZrO2 in thin zirconia films grown by electron beam evaporation is presented. X-ray powde r diffraction results show that the films are at the boundary of the amorph ous/crystalline state of the matter. Micro-region:, of unknown crystalline structures of ZrOz(2) are formed during the growth and are observed by tran smission and reflection electron diffraction. Two CaF2-type zircon oxides e xist inside the films. They are the known high temperature cubic phase with lattice parameter a = 5.09 +/- 0.08 A and an isostructural analogue with a = 5.40 +/- 0.10 A. Series of hexagonal and cubic close packed structures. believed to be related to the packing of clusters, are also detected. The e xistence of metastable zirconia structures is explained by Ostwald's rule o f stages. A comparison of some of the metastable oxide structures of ZrO2 f ilms with their isostructural analogues observed in SiO2 and SnO2 films is included.