1 Department of Energy Conversion and Storage, Technical University of Denmark2 Electrofunctional materials, Department of Energy Conversion and Storage, Technical University of Denmark
Chemical solution deposition is a versatile technique to grow oxide thin films with self-organized nanostructures. Morphology and crystallographic orientation control of CeO2 thin films grown on technical NiW substrates by a chemical solution deposition method are achieved in this work. Based on an enhanced understanding of the effect of oxygen partial pressure during film crystallization, a strong texture can be obtained on the surface of the CeO2 films annealed at temperatures as low as 900 °C followed by a two-step annealing procedure. Crystallization at high temperature (e.g., 1100 °C) in a reducing atmosphere leads to the formation of an oxygen deficient CeO2−x phase coexisting with a small amount of a polycrystalline CeO1.67 phase. Further surface phase and texture analysis by an electron backscattering diffraction technique reveals that the off-stoichiometric CeO2−x phase retains a fluorite structure but exhibits an alternative in-plane texture with eight fold symmetry on the surface. According to phase and texture stability studies, these off-stoichiometric phases gradually transform back to fully oxidized CeO2 with a 45° rotated cube texture during storage in ambient air. Moreover, the morphology of the CeO2 thin films is controlled by precisely regulating the film thickness and crystallization temperature. A temperature-induced transition from the commonly observed granular grain to an atomically flat surface is found in the CeO2–NiW constitution. Cross-sectional transmission electron microscope observation also reveals that this phenomenon is mainly attributable to the surface re-organization, which is strongly associated with the critical film thickness, crystallization temperature, reducing ability of the crystallization atmosphere as well as the interface properties.
Crystengcomm, 2013, Vol 15, Issue 19, p. 3816-3823