Thermal treatment effect of the oxidized La2CuO4+δ: The access of continuous and discontinuous Tc

Superconductive La2CuO4+δ with Tc ∼ 40 K has been obtained by chemical oxidation using NaClO solution. The oxygen-decrease processes have been studied during the thermal treatment processes at different temperatures. The material separates into discrete phases with different transition temperatures for samples treated at 100 °C, consistent with the oxygenation process reported previously. However, Tc decreases continuously in samples treated at 300 °C, similar to the superconducting properties of La2−xSrxCuO4. In addition, the coexistence of superconducting and antiferromagnetic phases cannot be observed in our samples. The interrelation between the transition temperature and the treatment conditions such as temperature and time is discussed.