A quantum molecular dynamics study of proton diffusion in SrTiO_3 and CaTiO_3

摘要

Protonic motion in cubic perovskite SrTiO_3 and CaTiO_3 is investigated by numerical simulations at higher temperatures. The protons are primarily found to form transient hydrogen bond complexes. The repulsive titanium/proton interaction causes a bending of the hydrogen bonds and, thus, aggravates proton transfer. However, as the proton interaction also extends to the next-next nearest oxygen sites the formation of transient, linear inter-octahedra hydrogen bonds, i.e. between the tips of neighbouring octahedra, is also possible. Whereas the time constants for proton reorientation are found to be of similar magnitude in both materials, the time constant for proton transfer is found to be larger by an order of magnitude in SrTiO_3. Furthermore, the numerical simulations yield an activation energy for proton diffusion of 0.50 +- 0.22 eV for SrTiO_3 and 0.42 +- 0.30 eV for CaTiO_3.