IN-SITU NEUTRON-DIFFRACTION STUDIES ON THE ELECTROCHEMICAL OXIDATION OF POLYCRYSTALLINE LA2CUO4

The electrochemical oxidation of La2CuO4 was studied at room temperatu re in an aqueous alcali electrolyte by in situ neutron diffraction on polycrystalline electrodes. Structure analysis was undertaken for seve ral phases with different oxidation levels at different temperatures. For the maximum oxidized phase with a T-c of 44 K an increased orthorh ombicity is observed. For this phase the superstructure reflections re lated to the tilting of the CuO6 octahedra were no longer observed eve n on cooling to 4 K. The structure refinements of the 44 K phase imply an average structure in the space group Fmmm with a partial lost of t he 3D-order of the CuO6 octahedra.