A quantum molecular dynamics study of the cubic phase of BaTiO 3 and BaZrO 3

Abstract

High proton mobility in perovskite-type oxides of composition ABO 3 strongly depends on the dynamics of the proton environment, especially on the fluctuations of the oxide ion separations. The dynamics of the oxide host lattices of the model materials BaTiO 3, and BaZrO 3 have been studied using quantum molecular dynamics simulations. The simulation method has already been shown to yield numerical results in agreement with experimental findings for the cubic phase of BaCeO 3. At elevated temperatures, rotational diffusion of the protons around the oxygen atoms in the plane perpendicular to the B-O-B axis is found. The free energy of the oxygen lattice vibrations is evaluated and the activation energy for proton transfer is estimated to be 0.45 eV for BaTiO 3, 0.69 eV for BaZrO 3, and 0.64 eV for BaCeO 3.