PRECISION NEUTRON-DIFFRACTION STUDY OF THE HIGH-T-C SUPERCONDUCTOR HGBA2CUO4+DELTA

A neutron-diffraction study of HgBa2CuO4+delta structure and its depen dence on extra oxygen content for delta between 0.06 and 0.19 has been carried out with four pure samples using high-resolution TOF and lamb da=const diffractometers at room temperature and T = 8 K. Sample chara cterization was done by measuring ac susceptibility, x-ray and EPR spe ctra, and by iodometric titration. A detailed analysis of atomic struc ture and the occupancy factors of mercury and oxygen was performed and showed the stoichiometric cation content. Extra oxygen was found only in the (1/2,1/2,0) position of the basal plane. T-c varied parabolica lly with delta and exhibited a maximum of 98 K at delta approximate to 0.12. The data obtained can be considered as evidence of the conventi onal anion doping mechanism with 2 delta holes per CuO2 layer.