Phase Equilibria, Crystal Structure, and Properties of Intermediate Oxides in the Sm2O3-SrO-CoO System

The phase equilibria in the (1)/2Sm2O3-SrO-CoO system were systematically studied at 1100 degrees C in air. Single-phase Sr1-xSmxCoO3-delta and Sr2-ySmyCoO4+delta solid solutions were obtained within the ranges of 0.05 <= x <= 0.50 and 0.9 <= y <= 1.3, respectively. XRD patterns of the single-phase samples were refined by the Rietveld method within the tetragonal structure (space group I4/mmm). Gradual substitution of strontium by samarium leads to a decrease of the unit-cell parameters and the unit-cell volume that can be explained by the size factor. An introduction of samarium into strontium cobaltite increases the oxygen content in Sr1-xSmxCoO3-delta. The variation of the electrical conductivity, Seebeck coefficient, and thermal expansion of Sr1-xSmxCoO3-delta and Sr2-ySmyCoO4+delta oxides vs. temperature were measured in air. The chemical reactivity of Sr1-xSmxCoO3-delta and Sr2-ySmyCoO4+delta, in contact with the solid electrolyte materials Ce0.8Sm0.2O2 and Zr0.85Y0.15O2, was examined. The projection of the isothermal-isobaric phase diagram (1100 degrees C, air) to the compositional triangle (Sm2O3)-Sm-1/2-SrO-CoO has been constructed.