Effects of doped acceptor ions on proton diffusion in perovskite oxides: a first-principles molecular-dynamics simulation

The effects of doped acceptor ions on proton diffusion in the protonic conductor Sc-doped are studied by means of a first-principles molecular-dynamics simulation. It is found that the proton forms an O-H bond with the neighbouring O ion, and that the frequency of the O-H stretching vibration depends on the position of the proton in the crystal. The frequencies obtained from our simulations are consistent with the experimental results obtained from the infrared-transmission spectra. It is shown that the position dependence of the O-H stretching vibration is caused by the electron density distribution in the Sc-doped . Near the Sc ion, electrons tend to localize around each ion causing higher frequencies, while, near the Ti ion, the electron density between the Ti and O ions is larger than that in the undoped crystal, giving lower frequencies.