ON THE OCCURRENCE OF A METASTABLE TETRAGONAL T'-PHASE IN A ZRO2-13.6 MOLE PERCENT MGO CERAMIC AND ITS MICROSCOPIC THERMAL EVOLUTION

The time-differential perturbed angular correlation technique has been used to investigate the thermal behavior of a ZrO2-13.6 mole % MgO ceramic between room temperature and 1423 K. Two different quadrupole hyperfine interactions corresponding to a tetragonal structure have been found to result on cooling the ceramic from the single-phase cubic field. One of them agrees with that depicting the pure t-ZrO2 tetragonal phase and the other one has been interpreted as describing a high-MgO-content nontransformable t'-ZrO2 phase. As temperature increases, the latter gives rise to a similar but fluctuating interaction related to the oxygen vacancies mobility and which shows a thermal behavior analogous to that already reported for the stabilized cubic ZrO2. Above 1100 K these dynamic t'-sites transform into pure tetragonal ones which behave ordinarily, suffering the t --> m phase transition when cooling to room temperature. Differences found between TDPAC results and information drawn from other techniques are discussed.