HOLE STATE DENSITY AND SUPERCONDUCTIVITY IN OXYGEN-DEFICIENT LA2-XSRXCUO4-Y AND YBA2CU3O7-DELTA

Oxygen K near-edge spectra measured by fluorescence yield were obtaine d for fully oxidized and oxygen-deficient YBa2Cu3O7-delta (1:2:3) and La2-xSrxCuO4-y (2:1:4). Two features occur just above the Fermi level, one near 530 eV (hybridized d states) and the other near 528 eV (oxyg en 2p holes). For 1:2:3 the oxygen dependence of energy and intensity of the two peaks is determined. The oxygen hole peak intensity has a c onstant non-zero value for 6.27 less than or equal to (7-delta) less t han or equal to 6.40 where the superconducting transition temperature T-c is below 5 K, then rises (as does T-c) as the oxygen content incre ases toward 7. These results are correlated with earlier Cu K edge mea surements which determined the Cu1+ content of similar samples. These quantitative bulk results can also be used as a calibration for estima ting the local oxygen content of the microstructure (e.g., grain bound aries) using electron energy loss spectroscopy. We also report oxygen K edge measurements of standard and oxygen-reduced 2:1:4 well into the ''overdoped'' region (0.35 less than or equal to x less than or equal to 0.60), and compare these results with those for 1:2:3.