The replacement of [HgO2](2-) by the tetrahedral sulfate anion [SO4](2-) in the Hg-1201 superconductorстатья
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Аннотация:The possibility of existence of a Hg1-xSxBa2CuO4+2x+delta solid solution [(Hg, S)-1201] was studied at 18 kbar and 920 degrees C, Monophasic samples were obtained in the range 0.00 less than or equal to x less than or equal to 0.15, where the unit cell parameters were found to vary from a = 3.8685(1) Angstrom, c = 9.4667(2) Angstrom for x = 0.00 to a = 3.9010(1) Angstrom and c = 9.3048(6) Angstrom for x = 0.15. Samples with x greater than or equal to 0.20 were polyphasic and the unit cell parameters of the [(Hg, S)-1201] phases were found to vary up to a = 3.9072(1) Angstrom, c = 9.2654(5) Angstrom for a nominal composition x = 0.30, The as-prepared phases with 0.00 less than or equal to x less than or equal to 0.05 were found to be nonsuperconducting due to overdoping, while superconductivity appeared at x = 0.10 (T-c,T-onset = 40 K). T-c increases with the amount of sulfate substitution due to the decrease of the average copper valence, For the annealed samples, the variation is opposite to that found for the as-prepared samples, T-c,T-onset being higher for the sulfur-free phase. Rietveld refinements of neutron powder diffraction data has determined approximate to 18% of the HgO22- dumbbells to be substituted by SO42- groups. In this structure the SO42- anion adopts an average S-O bond length that is slightly higher than those in BaSO4. (C) 1996 Academic Press, Inc.