First-principles study of structural and electronic properties of BaTiO_3(001) oxygen-vacancy surfaces

摘要

The structural and electronic properties of fully-relaxed BaTiO_3(001) surfaces with oxygen vacancies are investigated by first-principles calculations. The large displacements of ions deviated from their crystalline sites to lead to the formation of the surface rumpling have been obtained. Some in-gap Ti 3d states at about -1.0 eV below the Fermi level are observed in the Ti-terminated surface caused by the oxygen vacancies. For the Ba-terminated oxygen-vacancy surface, some in-gap Ti 3d states also move into the bulk mid-gap region to become partial occupied, and two different chemical states of Ba 5p states are found. One is attributed to the bulk perovskite Ba atoms and another one is caused by the relaxation of surface Ba atoms. The calculations are in agreement with experimental data from ultraviolet photoelectron spectroscopy and x-ray photoelectron spectroscopy studies.