Polymorphic Transformations of Zirconia.

摘要

The polymorphic transformations of zirconia are elucidated as displacive transformations originating from the softening or partial softening of appropriate elastic constants. From expansions of the free energy in powers of symmetry-adapted homogeneous strains, all the possible symmetry and thermodynamically allowed tranformation paths starting from the cubic and tetragonal parent phases are obtained. It is found that transformations that start from the cubic parent phase involve cubic variants and are necessarily of a discontinuous (first order) nature because of symmetry. However, transformations that start from the tetragonal parent phase do not involve cubic invariants. They can be of a discontinuous or continuous (higher than first order) nature depending on whether the fourth order invariants are negative or positive. 18 refs., 2 tabs. (ERA citation 13:036848)