DEPENDENCE OF SUPERCONDUCTING PROPERTIES ON THE CU-VALENCE DETERMINEDBY IODOMETRY IN HGBA2CUO4+DELTA

We have synthesized nearly single-phase HgBa2CuO4+delta samples with v arious oxygen contents, and systematically investigated the relationsh ip between the lattice parameters, the superconductivity transition te mperature (T-c) and the oxygen content determined by iodometry. Furthe rmore, the nominal copper valence values were calculated from the oxyg en content data by assuming constant valence values of +2.00 and -2.00 for mercury and oxygen, respectively. Both the a and c lattice parame ters were found to decrease monotonically with the Cu valence over a w ide range of +2.05-2.28. The obtained T-c versus Cu valence curve exhi bits a ''bell shaped'' correlation with the maximum in T-c at the Cu v alence of similar to +2.18.