First-principles study of band gap engineering via oxygen vacancy doping in perovskite ABB ^′O ₃ solid solutions

Oxygen vacancies in perovskite oxide solid solutions are fundamentally interesting and technologically important. However, experimental characterization of the vacancy locations and their impact on electronic structure is challenging. We have carried out first-principles calculations on two Zr-modified solid solutions, Pb(Zn _1/3Nb _2/3)O ₃ and Pb(Mg _1/3Nb _2/3)O ₃, in which vacancies are present. We find that the vacancies are more likely to reside between low-valent cation-cation pairs than high-valent cation-cation pairs. Based on the analysis of our results, we formulate guidelines that can be used to predict the location of oxygen vacancies in perovskite solid solutions. Our results show that vacancies can have a significant impact on both the conduction and valence band energies, in some cases lowering the band gap by 0.5 eV. The effects of vacancies on the electronic band structure can be understood within the framework of crystal field theory.