Microstructure of ZrO2–CeO2 hetero-multi-layer films grown on YSZ substrate

Multi-layer films of pure ZrO{sub 2} and CeO{sub 2} were grown using oxygen plasma assisted molecular beam epitaxy on yttria stabilized zirconia (YSZ) substrates. The microstructure of the film was analyzed using x-ray diffraction (XRD), conventional and high-resolution transmission electron microscopy (HRTEM), electron energy-loss spectroscopy (EELS), energy dispersive x-ray (EDX) elemental mapping, selected area electron diffraction, and dynamical electron diffraction calculations. The deposited pure CeO{sub 2} layers exist in the cubic fluorite structure, and the ZrO{sub 2} layers show a good epitaxial orientation with respect to the CeO{sub 2} layers. However, 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 reveals that these forbidden diffraction spots were contributed solely by the ZrO{sub 2} layers. Dynamical electron diffraction calculation based on the tetragonal phase of unity tetragonality (space group P4{sub 2}/nmc) with oxygen displaced along the c-axis does not match with the experimental pattern. Instead, a diffraction pattern calculated based on a cubic structure (space group P{bar 4}3m) for which the oxygen sub-lattice was displaced along the matches with the experimental data. It is further suggested that the displacement of the oxygen from the idealmore » (1/4, 1/4, 1/4) position was introduced during the film growth process.« less