First-principles study of defect formation energies in LaOXS2 (X = Sb, Bi)

We theoretically investigate defect formation energies in LaOXS2 (X = Sb, Bi) using first-principles calculation. We find that the oxygen vacancy is relatively stable, where its formation energy is higher in X = Sb than in X = Bi. An interesting feature of X = Sb is that the vacancy of the in-plane sulfur atom becomes more stable than in X = Bi, caused by the formation of an Sb2 dimer and the electron occupation of the impurity energy levels. The formation energies of cation defects and anion-cation antisite defects are positive for the chemical equilibrium condition used in this study. Fluorine likely replaces oxygen, and its defect formation energy is negative for both X = Sb and Bi, while that for X = Sb is much higher than X = Bi. Our study clarifies the stability of several point defects and suggests that the in-plane structural instability is enhanced in X = Sb, which seems to affect a structural change caused by some in-plane point defects.

Automated summary

We theoretically investigate defect formation energies in LaOXS2 (X = Sb, Bi) using first-principles calculation. Oxygen vacancy is found to be relatively stable, with higher formation energy in X = Sb than in X = Bi. An interesting feature of X = Sb is the increased stability of in-plane sulfur atom vacancy compared to X = Bi, due to the formation of an Sb2 dimer and electron occupation of impurity energy levels. Cation defects and anion-cation antisite defects have positive formation energies under the chemical equilibrium condition. Fluorine likely replaces oxygen, with negative defect formation energy for both X = Sb and Bi, but significantly higher for X = Sb. Our study clarifies the stability of several point defects and suggests enhanced in-plane structural instability in X = Sb, possibly causing structural changes due to in-plane point defects.