The effects of doped acceptor ions upon proton diffusion in Sc-doped samples were studied by means of first-principles molecular dynamics simulations. It was found that the proton formed an O-H bond with the neighboring O ion, and that the frequency of the O-H stretching vibration depended upon the position of the proton in the crystal. The frequencies which were deduced from the simulations were consistent with experimental results obtained from infra-red transmission spectra. It was shown that the positional dependence of the O-H stretching vibration was caused by the electron density distribution in the Sc-doped samples. Near to Sc ions, electrons tended to localize around each ion and produced a higher frequency while, near to Ti ions, the electron density between the Ti and O ions was larger than that in the undoped crystal; thus giving rise to lower frequencies.

F.Shimojo, K.Hoshino, H.Okazaki: Journal of Physics - Condensed Matter, 1998, 10[2], 285-94