Phase equilibria in the La–Ba–Co–O system

Phase equilibria in the La–Ba–Co–O system were studied at 1100°C in air. The existence of oxide phases LaCoO3, BaCoO3−y, Ba2CoO4, and La2BaO4 in quasibinary systems in air at 1100°C was found, in agreement with previous data. Two types of solid solutions were found in the quasiternary system: La1−xBaxCoO3−δ and (La1−zBaz)2CoO4. The homogeneity range of La1−xBaxCoO3−δ was found to be 0 ≤ x ≤ 0.8. As the content of alkali-earth metal (x) increased, a rhombohedral distortion of La1−xBaxCoO3−δ decreased; La0.55Ba0.45CoO3−δ had an ideal cubic structure. The composition of single phase samples of (La1−zBaz)2CoO4 composition was obtained for z = 0.300, 0.325, 0.350, and 0.375. These samples had the tetragonal K2NiF4-type structure.