HOLE STATES IN (CD0.5PB0.5)SR-2(CAXY1-X)CU2O7 STUDIED BY X-RAY-ABSORPTION SPECTROSCOPY

The hole distribution of underdoped and optimum doped states in (Cd0.5 Pb0.5)Sr-2(Ca(x)Y2(1-x))Cu2O7 compounds has been investigated by high- resolution oxygen K-edge and copper L-edge X-ray absorption near-edge- structure spectra. Near the oxygen 1s edge, a pre-edge peak with a max imum at approximate to 528.3 eV was found, which is ascribed to the ex citations of oxygen 1s electrons to 2p hole states located in the CuO2 planes. The intensity of this pre-edge peak increased with calcium do ping for 0 less than or equal to x less than or equal to 0.5. This dem onstrates that the chemical substitution of Ca2+ for Y3+ in (Cd0.5Pb0. 5)Sr-2(CaxY1-x)Cu2O7 gives rise to an increase in hole concentration w ithin the CuO2 planes and a change from a semiconductor to a supercond uctor with T-c up to 30 K. The results of the copper L-edge absorption are consistent with those observed for oxygen Is X-ray absorption.