Dopants and defects: Local structure and dynamics in barium cerates and zirconates

In this paper we present an overview of state-of-the-art EXAFS measurements and data analysis on Ba, Ce, Zr, Y, In and Gd local environments in Y:BaCeO3, In:BaCeO3, Gd:BaCeO3, Y:BaZrO3, and In:BaZrO3, at different temperatures, hydration degrees and doping levels. This approach allows to reach unprecedented insights on the peculiar role of the dopant, and its interactions with the other lattice defects. In particular, we evidence that each different dopant shows unique behavior, depending mainly on its electronic structure, and that the usual criterion of ionic radius matching is not useful to outline an effective doping strategy of proton-conducting perovskites. As what concerns the structure-property relationships, we evidence that the high dopant solubility, the high symmetry around the doped site, and the low local disorder, are detrimental for proton conductivity.