The surface termination of tetragonal BaTiO₃ is a critical factor that affects the properties of the oxide surface. In this work, we investigated the surface termination of single crystal BaTiO₃(1 1 1) using a combined Density Functional Theory (DFT) and X-ray photoelectron spectroscopy (XPS) analysis.

The surface stability of the stoichiometric (BaO₃ and Ti) and non-stoichiometric (BaO₂, O, BaO, O₂, Ba, and O₃) terminations of BaTiO₃(1 1 1) was studied using the DFT + U calculation. The result shows that the BaO₂ and O terminations have the lowest cleavage and surface energies, and thus predominate over other terminations in the phase diagrams. Thus, formations of surface defects on the stoichiometric termination effectively stabilize the polar surface of BaTiO₃(1 1 1). XPS of the O 1 s and Ti 2p regions of BaTiO₃(1 1 1) show the presence of the Ti³⁺ state and oxygen defects on the surface. Also, the DFT O 1 s chemical shifts of O₂*, O*, H₂O*, and OH* reveal that OH* species adsorbed on the defect sites of O-terminated BaTiO₃(1 1 1) reproduce the experimental XPS chemical shifts. Therefore, a combination of DFT and XPS indicates that BaTiO₃(1 1 1) prefers the OH*-covered O termination.

四方BaTiO ₃的表面终止是影响氧化物表面性质的关键因素。在这项工作中，我们使用组合密度泛函理论 (DFT) 和 X 射线光电子能谱 (XPS) 分析研究了单晶 BaTiO ₃ (1  1  1)的表面终止。

使用 DFT + U计算研究了 BaTiO ₃ (1 1 1) 的化学计量（BaO ₃和 Ti）和非化学计量（BaO ₂、O、BaO、O ₂、Ba 和 O ₃）末端的表面稳定性. 结果表明 BaO ₂和 O 末端具有最低的解理能和表面能，因此在相图中优于其他末端。因此，化学计量末端表面缺陷的形成有效地稳定了 BaTiO ₃ (1 1 1)的极性表面。BaTiO ₃的 O 1 s和 Ti 2 p区域的XPS     (1  1  1) 表明表面存在 Ti ³⁺态和氧缺陷。此外，O ₂ *、O*、H ₂ O* 和 OH*的 DFT O 1  s化学位移表明，吸附在 O 端 BaTiO ₃ (1 1 1)缺陷位点上的 OH* 物种再现了实验 XPS化学位移。因此，DFT 和 XPS 的组合表明 BaTiO ₃ (1 1 1) 更喜欢 OH* 覆盖的 O 终止。