Preparation of Complex Perovskite-like Oxides (Hg,Ce,Cu)(Sr,Ln,Ca)_2(Ln,Ca,Sr)Cu_2O_(6+#delta#)(1212) with Superconducting Properties

摘要

Results are reported concerning synthesis of isostructural superconducting and nonsuperconducting phases of compositions (Hg,Ce,Cu)(Sr,Ln)_2(Ln,Sr)Cu_2O_(6+#delta#)(Hg- 1212-Ln, Sr) (Ln = Pr; Nd, T_c= 50 K; Er; Lu, T_c = 75 K) and (Hg,Cu)(Sr,Ln,Ca)_2(Ln,Ca)Cu_2O_(6+#delta#) (Hg-1212-Ln, Ca) (Ln = Nd, Eu). Changes in the cation positions and structure depending on the particular lanthanide are traced. Based on the data obtained, dependences of the critical temperature on the composition and structural characteristics (lattice parameter, interatomic spacings, the extent of corrugation of the CuO_2 planes) are considered and the main crystal-chemical criteria responsible for the realization of superconducting properties of 1212-type phases are formulated. The validity of the concepts suggested is confirmed by synthesizing a superconducting phase (T_c = 108 K) of a total composition (Hg,Ce,Cu)(Sr,Ca)_2(Ce,Ca)Cu_2O_(6+#delta#).