A quantum molecular dynamics study of proton diffusion in SrTiO3 and CaTiO3

Protonic motion in cubic perovskite SrTiO3 and CaTiO3 is investigated by nu merical simulations at higher temperatures. The protons are primarily found to form transient hydrogen bond complexes. The repulsive titanium/proton i nteraction causes a bending of the hydrogen bonds and, thus, aggravates pro ton transfer. However, as the proton interaction also extends to the next-n ext nearest oxygen sites the formation of transient, linear inter-octahedra hydrogen bonds, i.e. between the tips of neighbouring octahedra, is also p ossible. Whereas the time constants for proton reorientation are found to b e of similar magnitude in both materials, the time constant for proton tran sfer is found to be larger by an order of magnitude in SrTiO3. Furthermore, the numerical simulations yield an activation energy for proton diffusion of 0.50+/-0.22 eV for SrTiO3 and 0.42+/-0.30 eV for CaTiO3. (C) 1999 Elsevi er Science B.V. All rights reserved.