Single-step synthesis and crystal structure of HgBa2CuO4+delta with a T-c of 97 K

Single-phase samples of HgBa2CuO4+delta (Hg-1201) have been synthesised from a reaction between a pre-synthesised precursor Ba2CuO3 and HgO, using a rapid-heat rapid-cool technique. This method yields high-duality samples with (as-synthesised) superconducting transition temperatures, T-c, up to 97 K, as defined by the onset of diamagnetism. The phase purity and crystal structure were identified by powder X-ray diffraction. In addition, powder neutron diffraction was employed to elucidate the structure, particularly the interstitial O3 site, which provides the ''holes'' required for inducing superconductivity in this material. We observe some disorder in this material, including the displacement of the O3 site from its ideal (0.5, 0.5, 0) position; this has not been observed in previous studies. A fourth oxygen site, labelled here O4, was located between two copper sites at (0.086, 0.5, 0).