First-principles molecular-dynamics simulation of proton diffusion in Sc-doped SrTiO3

The microscopic mechanism of proton diffusion in the protonic conductor Sc-doped SrTiO3 is studied by a first-principles molecular-dynamics simulation. It is shown that the proton forms an O-H bond with a neighboring O ion, and the frequency of the stretching vibration of the O-H bond is about 2800 cm(-1), which agrees reasonably well with the result of experiment. Two types of diffusion paths are observed: one is diffusion around the O ion while retaining the O-H bond, and the other is diffusion between the two neighboring O ions while switching the O-H bond. During the former type of diffusion, the stretching vibration proceeds and the length of the O-H bond is almost unchanged. The latter type of diffusion occurs frequently and quickly.