PHASE-STABILITY IN THE LA-BA-CU-O SYSTEM AT 98O-DEGREES-C AND 200-BAROXYGEN-PRESSURE

The LaO1.5-BaO-CuO pseudo-ternary phase diagram at 200 bar oxygen pres sure was explored by a solid-state reaction at 980 degrees C of numero us compositions. The phases which formed have been identified by X-ray diffraction. Significant differences from phases formed in air are no ticed. BaCuO2 and Ba2CuO2 are absent, Ba2CU3O5+delta is stabilized. La 2CuO4 remains stable, in addition LaCuO3 is formed in high pressure. B oth La2CuO4 and LaCuO, show an extended solubility with Ba2+ replacing La3+. The following phases do not form in a high P(O-2): LaBa2Cu3O7, LaBa2Cu4O8, La4BaCu5O13, La3Ba3Cu6O10, La2BaCu2O6 and La2BaCuO5. This is possibly because LaCuO3 is a highly oxidized phase (FCV approximate to 3.0), which is therefore strongly favored at elevated P(O-2) of 20 0 bar. Tie-lines have been worked out and a tentative phase diagram is presented.