CHEMICAL CONTROL OF UNDERDOPED AND OVERDOPED STATES IN Y(BA2-YSRY)CU3O6+DELTA

The chemical control of underdoped and overdoped states in the Y(Ba2-y Sry)Cu3O6+delta (delta similar to 0.1 and 0.9) compounds has been obse rved by high-resolution O K-edge X-ray-absorption near-edge-structure spectra. The chemical substitution of Sr for Ba in the fully-oxygenate d Y(Ba2-ySry)Cu3O6+delta (delta similar to 0.9) compounds gives rise t o high hole concentrations within both the CuO2 planes and the out-of- plane sites, leading to the overdoped state and the decrease in the su perconducting transition temperature from 92 K for y=0 to 84 K for y=0 .8. In contrast, an increase in the Sr content in the oxygen-deficient Y(Ba2-ySry)Cu3O6+delta (delta similar to 0.1) compounds did not indic ate superconductivity. The oxygen-deficient compounds exhibit the unde rdoped state due to the low hole concentration.