Nanostructural control in solution-derived epitaxial Ce1-xGdxO2-y films

摘要

A novel mechanism based on aliovalent doping, allowing fine tuning of the nanostructure and surface topography of solution-derived ceria films, is reported. While under reducing atmospheric conditions, non-doped ceria films are inherently polycrystalline due to an interstitial amorphous Ce2C3 phase that inhibits grain growth, a high quality epitaxial film can be achieved simply by doping with Gd3+ cations. Gd3+ <-> Ce4+ substitutions within the lattice are accompanied by charge-compensating oxygen vacancies throughout the volume of the crystallites acting as an efficient vehicle to reduce the barrier for grain boundary motion caused by interstitial Ce2C3. In this way, the original nanostructure is self-purified by pushing the amorphous Ce2C3 phase towards the free surface of the film. Once a full epitaxial cube-on-cube oriented ceria film is obtained, its surface morphology is dictated by the interplay between faceting on low energy {110} and/or {111} pyramidal planes and truncation of those pyramids by (001) ones. The development of the latter requires the suppression of their polar character which is thought to be achieved by charge compensation between the dopand and oxygen along < 100 > directions.