Understanding hydrogen in perovskites from first principles

Abstract The behavior of hydrogen in oxides is important to understand their functions; for example, some perovskites are fast proton conductors. Herein we study in detail the geometry, energetics, and chemical bonding of hydrogen in ABO3 perovskites from first principles. We find that hydrogen absorption to a lattice oxygen leads to structure distortion, especially in the (1 0 0) BO2 plane, and ~1.5% volume expansion. Density-of-states and crystal orbital Hamilton population (COHP) analyses indicate that the electron from hydrogen occupies the states at the conduction band minimum which correspond to the B O antibonding states and thereby weakens the B O covalent bonding. More interestingly, oxygen vacancy formation energy (OVFE), the integrated COHP of the B O bond, and the electronegativity difference between A and B are all found to be useful descriptors that correlate with hydrogen absorption energy (HAE).