Protonic motion in these cubic perovskites was investigated by numerical simulation at higher temperatures. The protons were primarily found to form transient hydrogen bond complexes. The repulsive titanium/proton interaction caused a bending of the hydrogen bonds and thus aggravated proton transfer. However, as the proton interaction also extended to the next-next nearest oxygen sites, the formation of transient linear inter-octahedra hydrogen bonds, i.e. between the tips of neighbouring octahedra, was also possible. While the time constants for proton reorientation were found to be of similar magnitude in both materials, the time constant for proton transfer was found to be larger by an order of magnitude in SrTiO3. The numerical simulations yielded an activation energy, for proton diffusion, of 0.50eV for SrTiO3 and 0.42eV for CaTiO3.

Quantum Molecular Dynamics Study of Proton Diffusion in SrTiO3 and CaTiO3. Münch, W., Kreuer, K.D., Seifertli, G., Majer, J.: Solid State Ionics, 1999, 125[1], 39-45