THE PHASE-STABILITY OF LA0.5SR0.5COO3-DELTA

In preparing ABO(3) compounds with A = La and Sr and B = Co or Mn, it has been found that strontium-substituted lanthanum cobaltite, La1-xSr xCoO3-delta, has much less tolerance for any variation in the A/B rati o than its manganite counterpart. This is specifically demonstrated fo r La0.5Sr0.5CoO3-delta where distinct phases readily appear on either sides of the A/B ratio for any small departure of this ratio from unit y. These secondary phases are clearly evidenced by scanning electron m icroscopy and X-ray diffraction. The same observations have been exten ded to various degrees of strontium substitution between 0.4 less than or equal to x less than or equal to 0.6. Additional data in regard to the main phase stability as a function of the oxygen partial pressure at temperatures up to 1425 degrees C have also been gathered. The (La 1-ySry)(2)CoO4-phase formed in this latter case is very similar to tha t due to the unbalance in the A/B ratio.