PHASE SEPARATIONS AND SUPERCONDUCTIVITY IN ELECTROCHEMICALLY INTERCALATED LA2CUO4+DELTA

We report the structure and superconducting properties of 110 degrees C annealed La2CuO4+delta for the nominal composition range 0 < delta < 0.12. At room temperature, two-phase regions were identified for 0.00 6 < delta < 0.047 and 0.075 < delta < 0.17. On cooling to low temperat ures, two coexisting T(c)s, similar to 15 and similar to 32 K, were ob served for delta > 0.065. The 15 K phase, which has a hole concentrati on p = 0.125, corresponds to an anomalous electronic state which is th e driving force for the low temperature electronic phase separations f or delta > 0.065. Our results indicate that there are simultaneous and continuous chemical and electronic phase separations in La2CuO4+delta as the excess oxygen content delta increases and/or the temperature d ecreases. The occurrences of superconductivity are intimately related to the phase separations.