Nonstoichiometry and relative stabilities of Y2Ti2O7 polar surfaces: A density functional theory prediction

Abstract

Density functional theory calculations were carried out to predict the surface structures and relative stabilities of (100) and (110) polar surfaces of a complex metal oxide, Y2Ti2O7. Based on a thermodynamic defect model, surface stabilities were evaluated as a direct function of stoichiometry and environmental factors, i.e. oxygen partial pressure and temperature. Calculations show that, as the oxygen partial pressure increases, the most stable termination of the (110) changes from Y/Ti-rich to O-rich. For the (100) surfaces, the most stable termination changes from Y/Ti-rich to stoichiometric, and then to O-rich, with increasing oxygen partial pressure. All variants of the (110) surfaces were found to be more stable than (100) surfaces. In particular, non-stoichiometric (110) surfaces are always more stable than their stoichiometric counterparts.