THE CRYSTAL-STRUCTURE AND SUPERCONDUCTIVITY OF 5CD0.5)(SR(0.9)LN(0.1))(2)(LN(0.7)CE(0.3))(2)CU2O9 (LN=PR, SM, EU, GD AND DY)

In this paper we report the crystal structure and superconductivity of 5Cd0.5)(Sr(0.9)Ln(0.1))(2)(Ln(0.7)Ce(0.3))(2)Cu2O9 (Ln = Pr, Sm Eu, G d and Dy). The lattice parameters of these compounds decrease nearly l inearly with the decrease of the average ionic radius of the rare-eart h element (Ln, Ce), and the superconducting transition temperatures of these compounds increase as the ionic radius of the rare-earth elemen t Ln decreases from Pr to Gd. (Pb0.5Cd0.5)(Sr0.9Gd0.1)(2)(Gd0.7Ce0.3)( 2)Cu2O9 has the highest T-c-values (T-c,T-onset = 49 K, T-c,T-zero = 3 8 K) which, to our knowledge, are also the highest T-c-values reported for any 1222 phase. The superconductivity of the system is affected b y many factors: (i) the coupling effect between CuO2 planes; (ii) the charge-carrier concentration in the CuO2 planes; and (iii) the degree of buckling of CuO2 planes.