Electronic and Magnetic Properties of Strongly Nonstoichiometric Solid Solutions Sr1 – xLax – yFe1 – zCozO3 – δ for a Pseudocapacitor Electrode

The content dependences of the electronic and magnetic properties of Sr_{1 – x}La_xFeO_{3 – δ}, Sr_{1 – x}La_{x ‒ y}FeO_3 ‒ δ and Sr_{1 – x}La_xFe_{1 – z}Co_zO_{3 – δ} cubic solid solutions are studied in the homogeneity region specified by δ = 0.05–0.35, \(x = 0.5\), \(y = 0.03\), 0.05, and z = 0.05–0.15 in the coherent potential approximation taking into account correlations on localized Fe-\({{t}_{{2g}}}\) and Co-\({{t}_{{2g}}}\) orbitals. Experimental electronic spectra and magnetic moments are reproduced using X-ray diffraction and thermogravimetry data for synthesized Sr_0.5La_0.5FeO_{3 – δ} nanopowders. Lanthanum doping of SrFeO_{3 – δ} strontium ferrite on the strontium sublattice expands significantly the region of oxygen nonstoichiometry \(\delta \) determining the accumulated charge Q. The introduction of cobalt into the iron sublattice and cation vacancies into the strontium sublattice effectively increases the electron conductivity, optimizes the energy range of oxidation/reduction \({{\Delta }_{{{\text{th}}}}}\), and increases the number of redox transitions in it. It is shown that the Sr_0.5La_0.5Fe_0.85Co_0.15O_2.65–2.95 solid solution, having a metallic/semimetallic electronic spectrum with the maximum number of redox transitions: Fe⁴⁺/Fe³⁺, Co⁴⁺/Co³⁺, Co³⁺/Co²⁺, and Co²⁺/Co¹⁺ in the interval of \({{\Delta }_{{{\text{th}}}}} \sim 0.65\) eV, is of interest for the creation of an electrode material for pseudocapacitors.