Crystallographic Analysis of the Cubic‐to‐Tetragonal Phase Transformation in the ZrO ₂ ‐Y ₂ O ₃ System

Abstract

The crystallography of diffusion‐induced and diffusionless cubic‐to‐tetragonal phase transformations in the ZrO 2 ‐Y 2 O 3 system is examined on the basis of the phenomenological crystallographic theory by adopting the lsqb;011rsqb; (0 1 1) twinning system as the lattice invariant deformation system. Numerical calculation indicates that the principal axes of the cubic phase are not exactly parallel to those of the tetragonal phase and that the habit plane orientation is sensitive to the lattice parameters of the cubic and tetragonal phases. The calculated results are compared with the observed crystallography of the tetragonal precipitates formed by diffusion and of the metastable tetragonal phase formed in a diffusionless manner. In many aspects, the present results were in good agreement with experimental observations. In particular, the crystallography and morphology of the so‐called “herringbone” structure are very well explained by the present analysis.