Cтруктура дефектов, электронная зонная структура и фазовый переход полупроводник--металл в кобальтите PrBaCo-=SUB=-2-=/SUB=-O-=SUB=-5.5-=/SUB=-: ab initio PAW-подход

Abstract

The calculations of electronic band structure of the cobaltite PrBaCo2O5+d for the content of oxygen near 5.5 have been performed using the first-principle PAW method. It has been shown that the semiconductor-metal transition near 5+d=5.5 is associated with the conversion of cobalt atoms in octahedral oxygen surrounding from high to low spin state and the similar atoms in pyramidal surrounding from the low to high spin state. The metal conductivity appears due to raising of the energy of pyramidal Co eg antibonding states. As a result these states turn up at the Fermi level thus defining the conductivity. The effect of oxygen content deviation from 5.5 on the band structure and conductivity has been studies. It is shown that the semiconductor-metal transition can be observed in the narrow range of 5+d below 5.5.