Anisotropic electronic structure and geometry of CaMnO3 perovskite with oxygen nonstoichiometry

The effects of oxygen nonstoichiometry on material formation, geometrical structure, and electronic structures together with carrier conductions of CaMnO3 perovskite are comprehensively studied in detail. Specifically, the formation energy of oxygen nonstoichiometry in CaMnO3 perovskite is 8.01eV. It has formation enthalpy of −7.10eV. The MnO6 octahedron is diminished along b and c, it is expanded along a. All Mn–O bindings tend to tilt and the MnO6 octahedron is distorted. The strength of Mn–O bindings parallel to the a–c plane is enhanced; the strength of Mn–O bindings parallel to the b direction is weakened. The band gaps are 0.804eV and 0.065eV for the CaMnO3 and CaMnO2.75, respectively. The work functions are 4.69eV and 2.58eV, respectively. The p orbital electrons form the upper valance bands and the d orbital electrons form the lower conduction bands. The Ca s, Mn d and O p electrons contribute to carrier conductions for CaMnO2.75 perovskite.