Model family of high-temperature superconductors: TlmCan-1Ba2CunO2(n+1)+m (m=1,2; N=1,2,3)

Abstract

We describe the structures and superconducting properties of six compounds in the Tl-Ca-Ba-Cu-O system of the general form, TlmCan-1Ba2CunO2(n+1)+m, where m=1 or 2 and n=1,2, or 3. One of the compounds displays the highest known superconducting transition temperature, Tc125 K. The structures of these compounds consist of copper perovskitelike blocks containing 1, 2, or 3 CuO2 planes separated by one or two Tl-O layers and thus form a model family of structures in which both the size and separation of the copper oxide blocks can be independently varied. The superconducting transition temperature increases with the number of CuO2 planes in the perovskitelike block for both the Tl-O monolayer and bilayer compounds. For each pair of compounds (m=1,2) with the same number of CuO2 planes (same n), the transition temperatures are similar but are consistently 15-20 K lower in the materials with single Tl-O layers. Variations in the transition temperatures in the double and triple CuO2-layer compounds are observed to correlate with increased densities of intergrowths of related structures. © 1988 The American Physical Society.