Stabilization and hyperfine characterization of metastable tetragonal ZrO₂

Abstract

Hydrolyzed ZrCl₄ and ZrO₂ · nH₂O have been used as starting compounds in a time-differential perturbed-angular correlation (TDPAC) investigation on the stabilization and thermal evolution of the metastable tetragonal form of ZrO₂. This phase, of quadrupole parameters very similar to those reported for the high temperature tetragonal form, emerges at moderate temperatures previous to the monoclinic phase, when starting from hydrolyzed ZrCl₄ and from ZrO₂ · 2H₂O treated previously at 673 K. Though in all cases zirconia appears initially as an amorphous compound characterized by unique hyperfine parameters, two different precursors have been observed to exist immediately previous to the occurrence of either the monoclinic or the metastable tetragonal crystal phases. Each of them exhibits a quadrupole frequency identical with and an asymmetry parameter higher than the ones characterizing the forthcoming corresponding crystal phases. A crystallization enthalpy of (33 ± 5) kJ/mol has been determined for the formation of the metastable tetragonal phase out of its precursor.