Hole Distribution in Underdoped and Overdoped Y(Ba(2-y)Sr(y)())Cu(3)O(6+delta) Compounds Studied by X-ray Absorption Spectroscopy.
The hole distribution of underdoped and overdoped states in the Y(Ba(2)(-)(y)()Sr(y)())Cu(3)O(6+)(delta) (delta approximately 0.1 and 0.9) compounds has been observed by high-resolution O K-edge X-ray-absorption near-edge-structure spectra. The chemical substitution of Sr for Ba in the fully oxygenated Y(Ba(2)(-)(y)()Sr(y)())Cu(3)O(6+)(delta) (delta approximately 0.9) compounds gives rise to high hole concentrations within both the CuO(2) planes and the out-of-plane sites, leading to the overdoped state and the decrease in the superconducting 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(Ba(2)(-)(y)()Sr(y)())Cu(3)O(6+)(delta) (delta approximately 0.1) compounds did not indicate superconductivity. The oxygen-deficient compounds exhibit underdoped state due to the low hole concentration.