On the possibility of replacing Hg by Cu in the HgBa 2CuO 4+δ phase synthesized under high-pressure

Abstract

To study the existence of the Hg 1- x Cu x Ba 2CuO 4+δ solid solution, samples with x = 0.00, 0.05, 0.10, 0.15, 0.20, 0.25, and 0.50, were synthesized using a high-pressure and high-temperature technique. These samples have been characterized by X-ray powder diffraction and AC susceptibility measurements. Only the samples with x = 0 and 0.05 were found to be monophase. The sample with x = 0, depending upon the preparation is non-superconducting or has a T c = 50 K. Its lattice parameters show that it is overdoped. All the other samples contain impurities, whose nature and relative quantities depend upon x and the compound used as extra Cu source. From the present results it can be deduced that Hg can in principle be replaced by Cu, but this replacement cannot be more than 10%. The discrepancy between the extra oxygen content determined by iodometric titration (0.13) and that determined by X-ray diffraction (0.20) and the low occupancy factor (or the relatively high thermal parameter) for the Hg cations is explained in terms of the incorporation of CO 3 −2 groups into the structure.