A new metastable phase with T/sub c/ of 32 K in La/sub 2/CuO/sub 4+/spl delta// system

A metastable superconducting phase with T/sub c/ of 32 K and /spl delta/=0.084 in La/sub 2/CuO/sub 4+/spl delta// system is reported in this paper. It is prepared by electrochemical oxidation for more than 2 months using a small constant current of 10 /spl mu/A. Its structure and physical properties are studied by X-ray diffraction, magnetic susceptibility and resistance measurements. This phase (we call it /spl beta/-phase) is different from the previously known one (we call it /spl alpha/-phase) that has the same T/sub c/ but 0/spl les//spl delta//spl les/0.055. After heat treatment at temperature T=80/spl deg/C, the /spl beta/-phase decomposes into two phases with T/sub c/'s of /spl sim/17 K and /spl sim/30 K, respectively. This kind of behavior is similar to the phase with T/sub c/ of 45 K. Our study shows that T/sub c/ increases with the intercalation rate, and oxygen distribution is an important factor for controlling superconducting properties.