Cooperative oxide-ion conduction in apatite-type lanthanum germanate—A first principles study

Abstract

The oxide-ion conduction mechanism in apatite-type lanthanum germanate, La₁₀(GeO₄)₆O₃, was theoretically investigated by the nudged elastic band method based on the first-principles calculations and the kinetic Monte Carlo (KMC) method. The dominant conduction process is the cooperative mechanism along the c axis with the lowest potential barrier of 0.64 eV, which is not reported previously in the lanthanum germanate system. The other responsible process was a different type of cooperative mechanism connecting the fast conduction channels with the calculated potential barrier of 0.76 eV. The oxide-ion conductivity and apparent activation energy of 0.71 eV in the crystal was statistically estimated by KMC simulations, which is coincident with the experimentally measured oxide-ion conductivities.