Phase Equilibria in the PrOx–CoOx–NiO System, Structure, and Oxygen Content in the Formed Oxides

Using the homogenizing annealing method and X-ray powder diffraction, it was shown that in the quasi-ternary PrOx–CoO–NiO system at 1373 K in air, two series of solid solutions are formed: PrCo $$_{{1 - x}}$$ NixO3 (0.0 ≤ x ≤ 0.4) with the orthorhombically distorted perovskite structure and Pr4Ni $$_{{3 - y}}$$ CoyO $$_{{10 - \delta }}$$ (0.7 ≤ y ≤ 1.5) with the Ruddlesden–Popper type structure with n = 3. The oxygen content in both series of solid solutions is close to stoichiometric. It is assumed that Ni2+ ions are predominantly located in octahedra located in the middle of the perovskite block, while Ni3+ and Co3+ ions are in octahedra adjacent to the rock salt layers. Phase diagrams of the PrOx–CoOx and PrOx–NiO systems were constructed in “T–composition” coordinates in air using literature data.