A NEW 50 K SUPERCONDUCTOR, Tl1+xBa2−x−yLayCuO5−δ, FIRST MEMBER OF THE SERIES TlA2Cam−1CumO2m+3

Abstract

New superconductors Tl 1+x Ba 2−x−y La y CuO 5−δ(x = 0, y = 0.6 and x = 0.25, y = 0.75) have been isolated, which exhibit a zero resistance below 50 K and a diamagnetic fraction volume ranging from 7% to 35%. Their tetragonal structure corresponds to the intergrowth of single perovskite layers with double rock-salt type layers. These latter slabs exhibit two original features, presence of oxygen vacancies and distribution of thallium over two sorts of sites. This particular behavior is discussed in terms of mixed valence of thallium, Tl(I)/Tl(III) taking into account the 6s2 lone pair of T1(I).