Phase equilibria in the LaCoO3-LaMnO3-BaCoOz-BaMnO3 system

The phase equilibria in the LaCoO3-LaMnO3-BaCoOz-BaMnO3 system were studied at 1100 degrees C in air by powder X-ray diffractometry of quenched sample s. The existence of three phases in the BaCo1-yMnyO3-delta system was confi rmed. Two of these phases are homogeneous in the range 0.15 less than or eq ual to y less than or equal to 0.30 and 0.38 less than or equal to y less t han or equal to 0,55, Both have hexagonal structures (space group P6(3)/mmc ), but 10-layered and 12-layered cells, respectively, The last phase, with approximate composition BaCo0.285Mn0.715O3-delta, was indexed on the basis of a 21H-structure with the unit cell parameters a = 5,7676(8) and c = 49.5 8(1) Angstrom (space group P6(3)/mmc), It was found that La1-xBaxMnO3+/-del ta phases with 0 less than or equal to x less than or equal to 0.10 possess O-orthorhombic structures (space group Pnma) and samples with 0.125 less t han or equal to x less than or equal to 0.30 have rhombohedral structures ( space group R (3) over bar c). The homogeneity range of solid solutions of the general formula La1-xBaxCo1-yMnyO3+/-delta with orthorhombic, rhombohed ral, and cubic structures has been determined, On the basis of the experime ntal results and earlier data, the pseudoquaternary phase diagram at 1100 d egrees C in air was constructed. (C) 2000 Academic Press.