New Tl-Ba-Ca-Cu-O (1234 and 1245) superconductors with T/sub c/<117 K

摘要

TlBa/sub 2/Ca/sub 3/Cu/sub 4/O/sub 11/ (1234) and TlBa/sub 2/Ca/sub 4/Cu/sub 5/O/sub 13/ (1245) superconductors have been synthesized for the first time. The compounds have T/sub c/ values of 116 approximately 122 K. The highest T/sub c/ value was obtained for the 1234 phase. These are single Tl-O layer compounds with less than half the Tl content of the previous 2223 phase. The structure of the compounds is a simple tetragonal phase with the lattice constants of a=b=3.85 AA and c=19.1 AA for the 1234 phase and a=b=3.85 AA and c=22.3 AA for the 1245 phase. The electron diffraction patterns and the lattice images from a high-resolution TEM have confirmed an oxygen-deficient layered-perovskite structure with the P4/mmm space group. The c-lattice constant follows the c-axis rule of a linear relation of c=6.3+3.2 n (n=the number of Cu-O layers), The T/sub c/ value is strongly related to the valence of Cu ion.