Control on the copper valence and properties by oxygen content adjustment in the LaCuO3-y system (0<=y<=0.5)

The LaCuO3-y perovskite is considered as the first member of the O1(n-1)n series of ''layered cuprates.'' Highly oxidized, stoichiometric LaCuO3 is stabilized under very high oxygen pressures, and was synthesized in a cubic-anvil-type high-pressure apparatus at 5 GPa and 1400 degrees C using excess amounts of KClO4 as an external oxidizing agent. Upon heating under ambient pressure the rhombohedral high-pressure phase loses oxygen yielding tetragonal, monoclinic, and orthorhombic forms of LaCuO3-y as intermediate products before the final decomposition into La2CuO4 and CuO or Cu2O around 800 degrees C. All three oxygen-deficient LaCuO3-y phases could be isolated and their stability limits and corresponding oxygen contents conveniently investigated by annealing stoichiometric LaCuO3 in a thermobalance of high sensitivity in order to in situ detect the exact amount of oxygen loss. The nominal copper valence values calculated from the oxygen contents are compared and discussed with XPS data as well as with the results evaluated from magnetic susceptibility measurements. (C) 1997 Academic Press.