Stable Surface Terminations of a Perovskite Oxyhydride from First-Principles

Successful synthesis of some perovskite oxyhydrides and their unique catalytic properties have recently attracted researchers' attention. However, their surface structure remains unclear. Here we identify stable surface terminations of a prototypical perovskite oxyhydride, BaTiO2.5H0.5, under catalytically relevant temperatures and pressures by using first-principles thermodynamics based on density functional theory. Five low-index facets, including (100), (010), (210), (011), and (211), and their various terminations for a total of 47 different surfaces have been examined for relative stability at different temperatures (700, 500, 300 K) and gas environments (10-15 ≤ PO2 ≤ 1 atm, 10-15 ≤ PH2 ≤ 100 atm). The most stable ones are found to be (010)-Ba2O2, (210)-Ti2O2, and (211)-Ba2O4H surface terminations. These polar surfaces are stabilized by charge compensation. This work provides important insights into the stable surfaces of perovskite oxyhydrides for future studies of their catalytic properties.