Dependence of superconducting properties on the Cu-valence determined by iodometry in HgBa2CuO4+δ

Abstract We have synthesized nearly single-phase HgBa 2 CuO 4+δ samples with various oxygen contents, and systematically investigated the relationship between the lattice parameters, the superconductivity transition temperature ( T c ) and the oxygen content determined by iodometry. Furthermore, the nominal copper valence values were calculated from the oxygen content data by assuming constant valence values of +2.00 and −2.00 for mercury and oxygen, respectively. Both the a and c lattice parameters were found to decrease monotonically with the Cu valence over a wide range of +2.05–2.28. The obtained T c versus Cu valence curve exhibits a “bell shaped” correlation with the maximum in T c at the Cu valence of ∼ +2.18.