Oxidation state of mercury in HgBa2(Ca0.86Sr0.14)2Cu3O8+δ studied by x-ray photoelectron spectroscopy

Hg 4f core levels of HgBa2(Ca0.86Sr0.14)2Cu3O8+δ (Hg-1223) and HgO were measured by x-ray photoelectron spectroscopy in order to demonstrate the oxidation state of mercury ions in the superconducting oxide. The binding energy of the Hg 4f7/2 level is found to be at 99.9 eV in HgO and 101.0 and 103.4 eV in Hg-1223. This result reveals that the oxidation state of Hg is definitely more than +2 and it exists in a mixed-valent state. The creation of charge carriers in Hg-1223 is discussed in terms of a charge transfer between Hg-Oδ and Cu-O layers. © 1995 The American Physical Society.