Localized Proton Motions in Acceptor-Doped Barium Zirconates

Acceptor-doped barium zirconates are currently accumulating considerable interest because of their high proton conductivity, especially in the intermediate-temperature range targeted for next-generation solid oxide fuel cells, combined with their excellent chemical stability. However, fundamental questions surrounding the proton conduction mechanism in these materials remain, for instance, regarding the nature of localized proton motions and how they depend on the local structural properties of the material. Here we investigate the nature of localized proton motions in the two acceptor-doped proton-conducting perovskites BaZr0.9M0.1O2.95 with M = Y and Sc, using quasielastic neutron scattering. We show the presence of pronounced localized proton dynamics, with mean residence periods on the time-scale of 1-30 ps and an activation energy of similar to 100 meV for both materials. In view of first-principles calculations as reported elsewhere the experimentally established dynamics could comprise footprints from proton transfers as well as O-H rotational motions in several different types of proton sites due to a range of various local proton sites present in both materials.