Distortion of the oxygen sublattice in pure cubic-ZrO₂

Multilayer films of pure ZrO₂ and CeO₂ were grown using molecular beam epitaxy on a yttria-stabilized zirconia (YSZ) substrate. Distinctive forbidden diffraction spots of (odd, odd, even) type were observed on the selected-area electron-diffraction patterns of the film. Dark-field imaging clearly revealed that these forbidden diffraction spots were solely due to the ZrO₂ layers. Comparison of the electron diffraction pattern with that simulated by dynamical calculations suggest that the pure ZrO₂ layers possess a cubic structure of space with the group P4 3m oxygen sublattice being displaced diagonally, rather than along the c axis as suggested for YSZ. Our results further suggest that the displacement of the oxygen from the ideal (¼, ¼, ¼) position might have been introduced during the film growth process.