Microscopic properties were investigated by means of perturbed -angular correlation spectroscopy. The method permitted the very accurate monitoring of absolute O vacancy concentrations which were in the ppm range. It was found that pentavalent Nb dopants led to the suppression of O vacancies and, in doped samples, only a small T3/2-dependence that was due to the zirconia lattice was identified. On the other hand, Y increased the number of point defects. An activation energy of 0.44eV was deduced for the trapping/detrapping process. An undoped sample was expected to exhibit no vacancies, and to behave like a Nb-doped one, as intrinsic point defects were expected to predominate only at higher temperatures. However, a non-negligible number of vacancies was detected. These were suspected to arise from impurities that were accidentally introduced during processing. However, an insufficient amount of impurity was found in order to explain the measured O vacancy concentration. Ceria-doped (1%) samples were studied in order to explain the occurrence of these vacancies. The samples could be calcined at 800C in the tetragonal phase, and the frequency monitored with increasing temperature. Beginning at 800C with no vacancies, it was found that they were introduced at temperatures ranging from 1000 to 1200C. The vacancy incorporation process was non-reversible, and the impurity levels were still below the detection limit in these high-purity samples. The experimental results indicated that the occurrence of the observed vacancy concentration could be correlated with enhanced grain growth, at temperatures as low as 800C.

R.Platzer, E.Karapetrova, M.O.Zacate, J.A.Gardner, J.A.Sommers, W.E.Evenson: Materials Science Forum, 1997, 239-241, 57-60