SUPERCONDUCTING PHASES OF LA2CUO4+DELTA PREPARED BY ELECTROCHEMICAL OXIDATION AT AMBIENT-TEMPERATURE

Superconducting phases in La2CuO4+δ prepared at ambient temperature by electrochemical oxidation have been investigated for the nominal composition range 0<δ<0.1. Consistent with previous reports, a stable superconducting phase with Tc∼32-34 K is observed for δ≤0.05. In contrast, samples with δ0.05 are found to be unstable either at room temperature or upon annealing between 25°C and 110°C. All phases with Tc higher than 34 K, such as Tc∼45 K phase, are metastable and only accessible under highly nonequilibrium intercalation conditions. A phase with Tc=15 K is also observed at a nominal hole concentration of p∼0.125, indicating that all of the observed Tc depressions in the cation substituted La2-x(Sr,Ba)xCuO4 and anion doped La2CuO4+δ at p∼0.125 are electronically driven and are of a common origin. © 1995 The American Physical Society.