The influence of oxygen deficiency on structural and electronic properties of layered superconductor (Fe₂As₂)(Sr₄V₂O_6−x )

By means of the first-principles FLAPW-GGA approach, we studied the influence of oxygen deficiency on the structural and electronic properties of the superconducting phase (Fe₂As₂)(Sr₄V₂O_6−x ). We find that the formation of vacancies in 2c sites of oxygen sublattice [when the initial tetragonal structure of the stoichiometric crystal (Fe₂As₂)(Sr₄V₂O₆) is kept] is energetically more preferable than in 4f sites, when orthorhombic distortions arise. The influence of oxygen vacancies on the structure of (Fe₂As₂) blocks is very insignificant; thus, using the known structural indicators, it is impossible to explain the observed drop of transition temperature T _C for oxygen-deficient systems by structural factors. On the other hand, the results of the band structure calculations allow us to assert that the vacancy-induced drop of T _C may be caused by the electronic factor, i.e., by the established decrease in N^tot(E _F) for the oxygen-deficient system.