Synthesis of various LaCuO3-y phases by a high-pressure technique and subsequent past-annealing treatments

The formation of the highly oxidized LaCuO3 perovskite is promoted by high oxygen pressures. In the present contribution the high oxygen pressures were generated in a cubic-anvil-type high-pressure apparatus using excess amounts of KClO4 as an external oxidizing agent. The high-pressure synthesis of the rhombohedral LaCuO3 was optimized in terms of the applied pressure and temperature, the synthesis time and the amount of the oxidizing agent. Essentially single-phase samples were obtained at 5 GPa and 1400 degrees C. Upon heating under ambient pressure the stoichiometric high-pressure form of LaCuO3-y loses oxygen yielding various oxygen-deficient phases as intermediates, and finally decomposes to La2CuO4 and CuO or Cu2O around 800 degrees C. The tetragonal, monoclinic and orthorhombic forms of oxygen-deficient LaCuO3-y could be isolated as pure phases by annealing in argon at temperatures of 280, 400 and 500 degrees C, respectively.