ANION DOPING AND SUPERCONDUCTING PROPERTIES OF HG-BASED SUPERCONDUCTING CU MIXED OXIDES

摘要

Different members of the HgBa_2Ca_(n-1)Cu_nO_(2n+n+δ) series with various oxygen concentration were prepared and characterized. Strongly overdoped high members of the series with n ≥ 3 were prepared only using high pressure high temperature technique. It was found that all members of the series exhibited similar cupola shaped dependencies of T_cvs. δ. Neutron powder diffraction experiments were carried out for monophase fluorinated HgBa_2CuO_4F_δ (T_c = 97 and 80 K) samples with different extra fluorine content. Fluorinated series also exhibits the cupola shaped behavior for the T_c vs. δ dependence, but this curve is shifted away from that one for the oxygenated series along the δ axis. NPD showed twice the amount of extra fluorine in comparison with those for the oxygenated Hg-1201 phases with close T_c's. An exchange of the extra oxygen by a double amount of fluorine causes an extended shortening of the apical Cu-O bond distances, while the in-plane distances, as well as T_c do not vary.