Effects of Dopant Ionic Radius on Cerium Reduction in Epitaxial Cerium Oxide Thin Films

Abstract

The role of trivalent rare-earth dopants in ceria epitaxial films on surface ion exchange reactivity and ion conductivity has been systematically studied. Single-crystal epitaxial films with unique crystal orientation and micro-structure nature have allowed us to rule out the influence of structural defects on both transport and surface ion exchange properties. The films conductivities were larger than those reported in literature for both polycrystalline ceramic pellets and crystalline films. An increase in oxygen vacancies and Ce<sup>3+</sup> concentration while decreasing the dopant ionic radius from La<sup>3+</sup> to Yb<sup>3+</sup> was observed, thus explaining the measured increased activation energy and enhanced surface reactivity. The more significant ability of smaller dopant ionic radius in releasing the stress strength induced by the larger Ce<sup>3+</sup> ionic radius allows promoting the formation of oxygen vacancies and Ce<sup>3+</sup>, which are two precious species in determining the efficiency of ion transport and surface ion exchange processes. This can open new perspectives in designing ceria-based materials in tailoring functional properties, either ion migration or surface reactivity, by rational cation substitutions.