Phase Equilibria, Crystal Structures, and Oxygen Nonstoichiometry of Complex Oxides Formed in the GdCoO₃–SrCoO_3–δ–SrFeO_3–δ–GdFeO₃ System

The phase relationships in the quasi-quaternary system GdCoO₃–SrCoO_3–δ–SrFeO_3–δ–GdFeO₃ at 1373 K in air have been studied. The homogeneity ranges and crystal structure of solid solutions with overall composition Gd_1–xSr_xCo_1–yFe_yO_3–δ have been determined. Depending on the concentration of introduced strontium and iron, the Gd_1–xSr_xCo_1–yFe_yO_3–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 Gd_1–xSr_xCo_1–yFe_yO_3–δ oxides. It has been shown that the oxygen content in the Gd_1–xSr_xCo_0.3Fe_0.7O_3–δ oxides, determined by thermogravimetric analysis, decreases with increasing temperature and strontium content. An isobaric-isothermal phase diagram for the GdCoO₃–SrCoO_3–δ–SrFeO_3–δ–GdFeO₃ system at 1373 K in air was constructed.