CRYSTAL-STRUCTURE AND SUPERCONDUCTIVITY OF NEW PB-BASED 1222-CUPRATE 0.5CD0.5)(SR0.9EU0.1)(2)(EU0.7CE0.3)(2)CU2O9+DELTA

A new superconductor 0.5Cd0.5)(Sr0.9Eu0.1)(2)(Eu0.7Ce0.3)(2)Cu2O9+delt a has been prepared. The compound has higher T-c values when it is syn thesized in Oz than in air. Besides, the O-2-synthesized sample exhibi ts metallic behaviour, while the air-synthesized sample exhibits semic onducting behaviour in their normal state. It has a typical metal-insu lator transition with the increase of the carrier concentration, which is proven by our calculation results of the bond valence sums of the Cu ions in the conducting CuO2 planes. (Pb0.5Cu0.5)(Sr7/8Eu1/8)2(Eu3/4 Ce1/4)2Cu(2)O(9) is an analogous compound of (Pb,Cd)-1222. (Pb,Cd)-122 2 has higher superconducting transition temperatures than (Pb,Cu)-1222 . This difference can be explained from the viewpoint of charge transf er between the charge reservoir (Pb,Cu)O layers and the conducting CuO 2 planes. The crystal structure of (Pb0.5Cd0.5)(Sr(0.9)Eu0. I)(2)(Eu0. 7Ce0.3)(2)Cu2O9+delta has been refined by the Rietveld method. The ref inement results indicate that both (Pb, Cd) and O(3) in the (Pb, Cd)O layer are displaced from their ideal sites.