Several experimental methods were used to study the dependence of large extrinsic O vacancy densities, in pure tetragonal ZrO2 powders, upon the details of powder preparation. Samples were made from oxychloride and nitrate precursor solutions, and perturbed angular correlation spectroscopy was used to determine the phase structure and density of O vacancies at 1200C. Scanning electron microscopy and X-ray diffraction were used to determine the grain size and morphology of samples which had been annealed at temperatures ranging from 1200 to 2000C. Neutron activation analysis was used to investigate the purity of the samples. The latter results showed that the samples contained cation impurities at levels which were considerably below 100ppm. The X-ray diffraction and scanning electron microscopy measurements showed that the grains were nm-sized, had a broad distribution, and grew from about 10nm at 200C to about 1μm at 1200C. The grain size and phase above 600C, and the morphology and density of O vacancies at 1200C, were strongly affected by the presence of Cl-containing vapor during annealing. Samples which were processed in a Cl-free atmosphere had large well-sintered grains and large (greater than 500ppm) O-vacancy concentrations at 1200C. Samples which were processed in flowing H2O-HCl vapor had smaller grains, a porous morphology and a low (less than 100ppm) vacancy density. All of the samples were loose powders which consisted of single grain particles below 1000C, and multiple-grain particles at 1200C.

Oxygen Vacancies in Pure Tetragonal Zirconia Powders - Dependence on the Presence of Chlorine during Processing. E.Karapetrova, R.Platzer, J.A.Gardner, E.Torne, J.A.Sommers, W.E.Evenson: Journal of the American Ceramic Society, 2001, 84[1], 65-70