Phase Equilibria and Structure of Solid Solutions in the La–Co–Fe–O System at 1100°C

Abstract

Phase equilibria in the La–Co–Fe–O system are studied at 1100°C in air using samples prepared by the citrate, nitrate, and conventional ceramic routes. The stability regions and structures of solid solutions in the La–Co–Fe–O system are determined by x-ray powder diffraction: LaCo1 – y Fe y O3 – δ (0 < y ≤ 0.25, sp. gr. R $${\bar 3}$$ c; 0.775 ≤ y< 1, sp. gr. Pbnm), Co1 – y Fe y O (0 < y ≤ 0.13, NaCl-type structure, sp. gr. Fm3m), and Fe3 – x Co x O4 (0.84 ≤ x ≤ 1.38, sp. gr. Fd3m). The structural parameters of phase-pure solid solutions are determined by the Rietveld method. The composition dependences of lattice parameters are presented for LaCo1 – y Fe y O3 – δ (0 < y≤ 0.25) and Fe3 – x Co x O4 (0.84 ≤ x ≤ 1.38). The 1100°C isotherm of the pseudoternary system La2O3–CoO–Fe2O3 in air is constructed.