Electrochemical oxidation of lanthanum cuprates. Superconductivity versus thermal treatment in La 2CuO 4+δ
Room-temperature electrochemical oxidation of La 2CuO 4 at the limiting value of 0.15 electrons per formula unit yields bulk superconducting materials with Tc values that depend on the applied potentials and the drying temperature. Superconducting fractions and structural parameters are also strongly dependent on moderate thermal treatments following the synthesis. We propose a reorganization of the charge carriers with temperature, involving charge transfer between Cu and intercalated oxygen atoms, to explain the analytical data obtained for various samples with different thermal treatments. Other cuprates also show the ability to intercalate oxygen. Thus, electrochemical oxidation of La 2- xSr xCaCu 2O 6-δ yields the oxygen stoichiometric phase that, although not superconducting, presents magnetic properties different from its precursor without a notable change in its structure.