Phase Equilibria in the LaCoO₃–LaMnO₃–BaCoO_z–BaMn O₃ System

Author： Cherepanov V.A. Filonova E.A. Voronin V.I. Berger I.F.

ISSN： 0022-4596

Source： Journal of Solid State Chemistry, Vol.153, Iss.2, 2000-09, pp. : 205-211

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Abstract

The phase equilibria in the LaCoO₃–LaMnO₃–BaCoO_z–BaMn O₃ system were studied at 1100°C in air by powder X-ray diffractometry of quenched samples. The existence of three phases in the BaCo_1-yMn_yO_3-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 BaCo_0.285Mn_0.715O_3-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 La_1-xBa_xMnO_3±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 La_1-xBa_xCo_1-yMn_yO_3±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.