Phase Equilibria, Crystal Structures, and Oxygen Nonstoichiometry of Complex Oxides Formed in the GdCoO3–SrCoO3–δ–SrFeO3–δ–GdFeO3 System

The phase relationships in the quasi-quaternary system GdCoO3–SrCoO3–δ–SrFeO3–δ–GdFeO3 at 1373 K in air have been studied. The homogeneity ranges and crystal structure of solid solutions with overall composition Gd1–xSrxCo1–yFeyO3–δ have been determined. Depending on the concentration of introduced strontium and iron, the Gd1–xSrxCo1–yFeyO3–δ oxides crystallize in orthorhombic (x = 0.1 and 0.4 ≤ y ≤ 1.0; x = 0.2 and y = 0.9, space group Pbnm), tetragonal (0.6 ≤ x ≤ 0.8 and 0.1 ≤ y ≤ 0.5, space group I4/mmm) or cubic (x = 0.9 and 0.1 ≤ y ≤ 0.9; 0.6 ≤ x ≤ 0.8 and 0.6 ≤ y ≤ 0.9, space group Pm $$\overline{3}$$ m) perovskite structure. Structural parameters were determined for all single-phase samples. It was found that an increase in the concentration of strontium and iron leads to an increase in the unit cells parameters of the Gd1–xSrxCo1–yFeyO3–δ oxides. It has been shown that the oxygen content in the Gd1–xSrxCo0.3Fe0.7O3–δ oxides, determined by thermogravimetric analysis, decreases with increasing temperature and strontium content. An isobaric-isothermal phase diagram for the GdCoO3–SrCoO3–δ–SrFeO3–δ–GdFeO3 system at 1373 K in air was constructed.