A new high-T_c superconducting intercalation compound

A new high-T_c superconducting intercalation compound, AgIBi₂Sr₂CaCu₂O_y, has been prepared either by reacting the silver metal directly with Bi₂Sr₂CaCu₂O_y powders under P(I₂) ∼ 1atm. at 190°C or by the intercalation reaction between the iodine-intercalated Bi₂Sr₂CaCu₂O_y and AgI. According to the X-ray diffraction analysis, the observed basal increase of 7.35 Å upon silver iodide intercalation indicates that the lattice expansion for AgIBi₂Sr₂CaCu₂O_y is twice as large as that for the first-staged iodine-intercalated Bi₂Sr₂CaCu₂O_y (Δd = 3.6 A ̊). Such a result suggests the gallery contains a double layer of iodine. A slight decrease in T_c for the AgIBi₂Sr₂CaCu₂O_y (T_c ≈ 63K) compared to the pristine (T_c ≈ 76K) has been observed by the d.c magnetic susceptibility measurements. The X-ray absorption spectroscopic results show that there is no charge-transfer between guest species (AgI) and host lattice. It confirms again that interblock-coupling has little effect on the superconductivity, since the T_c is not significantly evolved upon AgI intercalation with a large lattice expansion along the c-axis which is perpendicular to the (Cu-O) superconducting layers.