Phase equilibria and crystal structure of complex oxides in the La-Sr-Co-Ni-O system

Phase equilibria in the La-Sr-Co-Ni-O system were studied in air at 1100degreesC. The samples for the study were synthesized by the standard ceramic and citrate processes. The limiting solubility and structure of La1-xSrxCo1-yNiyO3-delta and (La1-xSrx)(2)Co1-yNiyO4 solid solutions were determined by X-ray powder diffraction analysis. La1-xSrxCo1-yNiyO3-delta solid solutions with 0 less than or equal to x less than or equal to 0.5 have a distorted rhombohedral perovskite-like structure (R (3) over barc space group). An increase in the strontium concentration reduces the rhombohedral distortions, and the compounds with x > 0.5 have an ideal cubic structure (Pm3m space group). (La1-xSrx)(2)Co1-yNiyO4 crystals have a tetragonal K2NiF4 type unit cell (14/mmm space group). The relationships between unit cell parameters and compositions were obtained for single-phase La1-xSrxCo1-yNiyO3-delta and (La1-xSrx)(2)Co1-yNiyO4 samples. The existence regions of La1-xSrxCo1-yNiyO3-delta and (La1-xSrx)(2)Co1-yNiyO4 solid solutions were distinguished on P-T phase diagrams.