PHASE-SEPARATION AND SUPERCONDUCTIVITY IN LA2CUO4- EFFECTS OF OXYGEN DIFFUSION(DELTA )

In oxygen-annealed LaCuO4+delta (delta approximately 0.03), bulk magne tization measurements show an increase of approximately 4K in the supe rconducting T(c) when the sample is cooled slowly through a narrow tem perature range near 195K. At this temperature, La-139 NQR spectra exhi bit a concomitant appearance of an anomalous feature associated with t he metallic phase whose spectral weight increases with cooling rate. T he data suggests a distribution of local structures and annealing-depe ndent volume fraction in this part of the sample. Interpretation of th ese results in terms of oxygen diffusion in a phase separated material is considered and a picture consistent with the observed changes in T (c) is obtained. The activation energy of oxygen diffusion derived fro m the model, Q approximately 0.25 eV, is in the same order of magnitud e as the results obtained in La2-xSrxCuO4-y.