Structure and superconductivity in Fe_xCu_(1-x)Ba_2YCu_2O_(7 + y) superconductors synthesized by high pressure

摘要

Comprehensive studies of X-ray diffraction, oxygen content, superconductivity and Moessbauer effect have been made on Fe_xCu_(1-x)Ba_2YCu_2O_(7 + y) superconductors (0.00 ≤ x ≤ 0.70) synthesized by ambient (AM) and high pressure (HP). Results indicate that all the HP-samples have tetragonal structure, smaller lattice parameter c and unit-cell volume than the AM-samples. The studies of oxygen content, and Moessbauer spectroscopy indicate that the HP-samples have higher oxygen content, carrier concentration and average valence of Fe than the AM-samples. Moreover, for the HP-samples more Fe atoms located in CuO_x chains have fivefold-oxygen coordination. These are important reasons for the enhancement of T_c in the HP-samples.