High-resolution neutron-diffraction experiments have been performed to study the structural changes of ${\mathrm{ZrO}}_2$ induced by ${\mathrm{CeO}}_2$ doping. The crystal structures of monoclinic [P$2_1$/c, Z=4] and tetragonal [P$4_2$/nmc, Z=2] phases for ${\mathrm{ZrO}}_2$–X mol % ${\mathrm{CeO}}_2$ (X=0, 2, 5, 8, 10, 12, and 15) have been refined by the Rietveld analysis of the diffraction patterns measured at 298 K. The unit-cell parameters change anisotropically with an increase of ${\mathrm{CeO}}_2$ content X. In the monoclinic phase ${\mathit{a}}_{\mathit{m}}$ and ${\mathit{c}}_{\mathit{m}}$ increase considerably while ${\mathit{b}}_{\mathit{m}}$ shows a rather small increase with increasing X where the suffix m denotes the monoclinic phase. The angle ${\mathrm{\beta }}_{\mathit{m}}$ decreases with increasing X. The thermal ellipsoids also show large anisotropies, which correlate strongly with the directions of the movements of oxygen ions during the phase transition. The unit-cell parameters and the atomic positions discontinuously change during the monoclinic-tetragonal phase change. The crystal structure of monoclinic phase approaches that of tetragonal phase with an increase of X: (1) the length of ${\mathit{a}}_{\mathit{m}}$ approaches that of ${\mathit{b}}_{\mathit{m}}$ with increasing X, (2) the angle ${\mathrm{\beta }}_{\mathit{m}}$ decreases with X, and (3) all positional parameters of the monoclinic phase approach those of the tetragonal structure.

• Received 12 December 1994

DOI:https://doi.org/10.1103/PhysRevB.51.8018