Electronic and local structural properties of the Bi2Sr2(Ca1-xYx)Cu2O8+δ family of materials, studied by X-ray absorption spectroscopy

The hole distribution of overdoped, optimum-doped and underdoped states in the series Bi2Sr2(Ca1-xYx)Cu2O8+delta compounds has been investigated by high-resolution O K-edge and Cu L-edge X-ray absorption near-edge-structure (XANES) spectra. Near the O 1s edge, a well-pronounced pre-edge peak with maximum at similar to 528.3 eV is found and is ascribed to the excitations of O 1s electron to O 2p hole states located in the CuO2 planes. The intensity of this pre-edge peak decreases as the Y doping increases, demonstrating that the chemical substitution of Y3+ for Ca2+ in Bi2Sr2(Ca1-xYx)Cu2O8+delta gives rise to a decrease in hole concentrations within the CuO2 planes. The results from the Cu L-edge X-ray absorption spectra are consistent with those from O Is X-ray absorption spectra. The local structure of the pyramidal CuO5 in Bi2Sr2(Ca1-xYx)Cu2O8+delta has been determined from extended X-ray absorption fine-structure (EXAFS) spectra. It was found that the axial Cu-O bond distances contract and the equatorial Cu-O bond distances expand as the Y content increases. Such results are strongly correlated to a decrease in the hole concentration within the CuO2 plane, which controls the superconductivity.