Preparation of complex perovskite-like oxides (Hg,Ce,Cu) (Sr,Ln,Ca)(2)(Ln,Ca,Sr)Cu2O6+delta(1212) with superconducting properties

Results are reported concerning synthesis of isostructural superconducting and nonsuperconducting phases of compositions (Hg,Ce,Cu)(Sr,Ln)(2)(Ln,Sr)Cu 2O6+delta (Hg-1212-Ln, Sr) (Ln = Pr; Nd, T-c = 50 K; Er; Lu, T-c = 75 K) an d (Hg,Cu)(Sr,Ln,Ca)(2)(Ln,Ca)Cu2O6+delta (Hg-1212-Ln, Ca) (Ln = Nd, Eu). Ch anges in the cation positions and structure depending on the particular lan thanide are traced. Based on the data obtained, dependences of the critical temperature on the composition and structural characteristics (lattice par ameter interatomic spacings, the extent of corrugation of the CuO2 planes) are considered and the main crystal-chemical criteria responsible for the r ealization of superconducting properties of 1212-type phases are formulated . The validity of the concepts suggested is confirmed by synthesizing a sup erconducting phase (T-c = 108 K) of a total composition (Hg,Ce,Cu)(Sr,Ca)(2 )(Ce,Ca)Cu2O6+delta.