High resolution O K-edge X-ray-absorption near-edge-structure (XANES) spectra for the series of new Hg-based Sr-containing 1212-typed (Hg0.5Pb0.5)Sr2(Ca1-xY x)Cu2O7 superconductors (x = 0.3 ∼ 0.7) were measured using a bulk-sensitive total-X-ray-fluorescence-yield technique. Near the O 1s edge, the pre-edge peak with maxima at ∼ 528.3 eV is ascribed to transitions into O 2p holes located in the CuO2 planes. The intensity of this pre-edge peak monotonically increases with increasing doping level of Ca2+ into the Y3+ sites. The effect of chemical substitution of Ca2+ for Y3+ in (Hg0.5Pb0.5)Sr2(Ca1-xY x)Cu2O7 is to induce O 2p hole states in the CuO2 planes near the Fermi level which cause an increase of Tc from 15 K for x = 0.6 to 90 K for x = 0.3. Moreover, the generation of O 2p holes within the CuO2 planes is probably responsible for inducing a transition from a semiconductor to a superconductor.
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Condensed Matter Physics
- Energy Engineering and Power Technology
- Electrical and Electronic Engineering