Proton Diffusion in Perovskite-Type Oxides Based on Small Polaron Model

The ground state energy and the wavefunction of proton in the cubic perovskite-type oxides ABO 3 are studied by using the double-well potential constructed from the one-dimensional O–H–O bond. We have found that when the O–O separation between the nearest neighbor oxygens becomes lower than 2.9 A the proton wavefunction spreads over the double-well potential and the proton transfers between the minimum sites in the double-well potential. We have calculated the activation energy E a for the proton transfer by using the small polaron model coupled with the lattice vibration of the O–B–O bond-bending mode. The calculated activation energy is found to be E a =0.56 eV for the cubic ABO 3 . We have also found the B-atom mass dependence that E a decreases with the B-atom mass in the O–B–O bond-bending mode. This B-atom mass dependence of E a is similar to that shown in the deformed perovskite-type oxides ABO 3 .