A new metastable phase with T-c of 32K in La2CuO4+delta system

A metastable superconducting phase with T-c of 32K and delta =0.084 in La2C uO4+delta system is reported in this paper. It is prepared by electrochemic al oxidation for more than 2 months using a small constant current of 10 mu A. Its structure and physical properties are studied by X-ray diffraction, magnetic susceptibility and resistance measurements. This phase (we call it beta -phase) is different from the previously known one (we call it alpha -phase) that has the same T-c but 0 less than or equal to delta less than o r equal to0,055, After heat treatment at temperature T=80 degreesC, the P-p hase decomposes into two phases with T-c's of similar to 17K and similar to 30K, respectively. This kind of behavior is similar to the phase with T-c of 45K, Our study shows that T-c increases with the intercalation rate, and oxygen distribution is an important factor for controlling superconducting properties.