DETERMINATION OF THE STRUCTURE OF THE CUBIC PHASE IN HIGH-ZRO2Y2O3-ZRO2 ALLOYS BY CONVERGENT-BEAM ELECTRON-DIFFRACTION

Convergent-beam electron diffraction (CBED) was used to determine the space group of 9.9 and 18 mol.% Y2O3-stabilized cubic ZrO2 single crystals. The result (space group, P43mBAR) is different from the known tetragonal structure (space group, P4(2)/nmc) present in lower solute (3.2 mol.% Y2O3) alloys, and the cubic structure (space group, Fm3mBAR) traditionally assumed for cubic ZrO2. The oxygen sublattice of the cubic structure is distorted from Fm3mBAR, relative to the cation sublattice, by displacements along the [111] directions. Computer simulations of the CBED patterns agree with experiment and suggest an anion displacement of about 0.3 angstrom from the {1/4,1/4.1/4} positions of the ideal fluorite structure.