Phase Equilibria in the LaCoO3–LaMnO3–BaCoOz–BaMnO3 System

Abstract

The phase equilibria in the LaCoO3–LaMnO3–BaCoOz–BaMnO3 system were studied at 1100°C in air by powder X-ray diffractometry of quenched samples. The existence of three phases in the BaCo1−yMnyO3−δ system was confirmed. Two of these phases are homogeneous in the range 0.15≤y≤0.30 and 0.38≤y≤0.55. Both have hexagonal structures (space group P63/mmc), but 10-layered and 12-layered cells, respectively. The last phase, with approximate composition BaCo0.285Mn0.715O3−δ, was indexed on the basis of a 21H-structure with the unit cell parameters a=5.7676(8) and c=49.58(1) Å (space group P63/mmc). It was found that La1−xBaxMnO3±δ phases with 0≤x≤0.10 possess O-orthorhombic structures (space group Pnma) and samples with 0.125≤x≤0.30 have rhombohedral structures (space group R3c). The homogeneity range of solid solutions of the general formula La1−xBaxCo1−yMnyO3±δ with orthorhombic, rhombohedral, and cubic structures has been determined. On the basis of the experimental results and earlier data, the pseudoquaternary phase diagram at 1100°C in air was constructed.