Structure and properties of Tl_0.5Pb_0.5Sr₂Gd_2−xCe_xCu₂O_9−δ

A systematic study of the Tl_0.5Pb_0.5Sr₂Gd_2−xCe_xCu₂O_9−δ system has revealed the existence of a pure phase in the compositional range 0.0 ≤ x ≤ 0.6 crystallizing in the 1222 structure. It has an intersheet distance of approximately 6 Å, a value much higher than those found in other cuprates with double CuO₂ sheets interleaved by a single fluorite layer. Superconductivity has been observed in the range 0.1 ≤ x ≤ 0.4 with a T_c of 45 K and a superconductive volume fraction up to 20% for the optimal composition. An interesting variation of the superconducting properties of the above system with the composition, i.e. cerium content, has also been noticed. A possible dependence of superconductivity on the coupling between CuO₂ sheets in the layered cuprates has been pointed out to bring out a correlation between structure and properties.