Negatively charged hydrogen at oxygen-vacancy sites in BaTiO3: Density-functional calculation

Abstract

With a specific focus on defects formed from H atoms and oxygen vacancies ( V O ) in perovskite-type oxide, stability and stable valence states of complex defects formation processes within BaTiO 3 are studied by using first-principle density-functional theory calculations. In our findings, H atoms diffuse as protons ( H + ) into interstitial sites in BaTiO 3 , whereas these atoms when trapped at centers of V O sites convert to negatively ionized states ( H − ) . We also find that H atom trapping at V O sites occurs only in n-type carrier-rich environments without carrier compensation of V O 2 + and H + . If carrier electrons are compensated, H + ions are excluded from V O 2 + sites due to the repulsive Coulomb potential existing between the H + ion and the positively charged V O 2 + site. Difficulties in the calculation of the diffusion-energy diagram for H atoms, involving essential changes in the stable valence states during the diffusion process, are discussed and a practical solution is presented.