PHASE-SEPARATION AND SUPERCONDUCTIVITY IN SUPEROXYGENATED LA2-XSRXCUO4+DELTA

La2-xSrxCuO4+delta with x = 0.01, 0.025, 0.050, 0.10 and 0.16 and with excess oxygen delta incorporated using high-pressure O2 anneals has b een examined using neutron diffraction data. Various models were fit b y Rietveld least-squares refinement, with the maximum amount of delta being only of the order of 20 times the standard deviation. Delta is l argest for x near 0, is zero for x = 0.10 and is intermediate for x = 0.16. Only the sample with x - 0.01 shows distinct phase separation in to a nearly stoichiometric phase with delta almost-equal-to 0 and an o xygen-rich superconducting phase as the temperature is lowered.