The relation between crystal structure and the formation and mobility of protonic charge carriers in perovskite-type oxides: A case study of Y-doped BaCeO3 and SrCeO3

Proton conductivity phenomena in 10% Y-doped barium and strontium cerate ar e investigated experimentally and by quantum molecular dynamics simulations . In particular the impact of deviations from the cubic perovskite structur e on the formation and mobility of protonic charge carriers is investigated . For Y: SrCeO3, which shows a larger deviation from the ideal cubic perovs kite structure, the concentration and mobility of protonic defects is signi ficantly lower than for Y:BaCeO3. The first is due to the decay of the oxyg en position into two sites, only one of which is involved in the formation of protonic defects. The symmetry reduction also leads to the formation of different one-dimensional proton diffusion paths, and unfavourable jumps be tween such paths are supposed to control the macroscopic proton diffusion c oefficient in Y:SrCeO3. The analysis suggests the formation of strong but t ransient hydrogen bonds and inter-octahedra proton transfer between vertice s for SrCeO3 in contrast to just intra-octahedra proton transfer for BaCeO3 . Whereas for BaCeO3 the proton transfer step is identified to be rate-limi ting at T = 1000 K, for SrCeO3 both proton transfer and reorientation are f ound to be of similar magnitude.