Revisiting the Low-Index Surfaces of LaCoO3 with a Passivation Strategy

A proper modeling is essential for calculating the surface properties of complex oxides, for example, perovskite oxides. Many studies have shown that traditional selections of slab models, either symmetric or asymmetric ones, may vary the calculated results of the polar surfaces, which will finally affect the perception of surface properties. To solve this issue, we proposed a passivation method to handle the complex polar surfaces, where the pseudo-atoms with fractional charges were used to balance non-zero net charges on one side of the surfaces. Based on this method, we revisited the low-index surfaces of LaCoO3, including (1 (1) over bar 02), (1 (1) over bar 04), and (0001) surfaces, with different terminations. The results suggested that the (1 (1) over bar 02)-LaO, (1 (1) over bar 02)-CoO2, and (0001)-LaO3 terminations were stable surfaces in different O and Co chemical environments. The oxygen vacancy formation energies (EOv) of the (1 (1) over bar 02)-LaO and (1 (1) over bar 02)-CoO2 terminations were also evaluated. Different from the unpassivated cases, the E-Ov of the passivated LaO and CoO2 terminations converged rapidly when slab thickness increased. The upward shift trend of the E-Ov after passivation was more consistent with the experimental results. The electronic structure analysis indicated that the oxygen vacancy mainly changed the valence state of the surrounding Co atoms. This work provides a more accurate calculation method, which may benefit the study on catalytic properties of complex oxides.

Automated summary

Proper modeling is crucial for calculating surface properties of complex oxides, such as perovskite oxides. A passivation method was proposed to handle complex polar surfaces, using pseudo-atoms with fractional charges to balance non-zero net charges. The study on LaCoO3 surfaces with different terminations showed that (1 (1) over bar 02)-LaO, (1 (1) over bar 02)-CoO2, and (0001)-LaO3 terminations were stable surfaces in different chemical environments. The passivated terminations also showed consistent oxygen vacancy formation energies and electronic structure changes with experimental results.