Control on the Copper Valence and Properties by Oxygen Content Adjustment in the LaCuO3−ySystem (0≤y≤0.5)

The LaCuO{sub 3-y} perovskite is considered as the first member of the 01 (n-1)n series of {open_quotes}layered cuprates.{close_quotes} Highly oxidized, stoichiometric LaCuO{sub 3} 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 KClO{sub 4} as an external oxidizing agent. Upon heating under ambient pressure the rhombohedral high-pressure phase loses oxygen yielding tetragonal, monoclinic, and orthorhombic forms of LaCuO{sub 3-y} as intermediate products before the final decomposition into La{sub 2}CuO{sub 4} and CuO or Cu{sub 2}O around 800{degrees}C. All three oxygen-deficient LaCuO{sub 3-y} phases could be isolated and their stability limits and corresponding oxygen contents conveniently investigated by annealing stoichiometric LaCuO{sub 3} in a thermo-balance 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.