Abstract
We have synthesized new Be-free Tl-based superconductor (Tl1-xHgx)(2)Sr2Ca2Cu3Oy using high-pressure high-temperature technique. These compounds are chemically and structurally stabilized by partial substitution of Hg for Tl. While Hg-free compound is multi-phased, Hg-doped compounds (x = 0.35-0.65) were nearly single phased and found to be superconducting with T-c's of 80-103 K. Electron diffraction and transimission electron microscope observations have revealed a body centered tetragonal unit cell isostructural with Ba-containing Tl-2223 phase with the Be-sites occupied by Sr. From structural refinements of the XRD data for x = 0.35, it was found that Sr and Cu sites are fully occupied, whereas the Tl-site and the Ca-site are partially occupied by Cu and Tl, respectively. Reducing treatments in Ar/H-2 atmosphere were found to be effective in enhancing T-c up to 116 K for x 0.35.