New members in the family of Hg and Tl based superconductors Hg1− xTlxBa2( Ca0.86Sr0.14) 2Cu3O8+ δ

Abstract

A new family of superconducting cuprate oxides based on mercury and thallium, Hg 1− x Tl x Ba 2( Ca 0.86 Sr 0.14) 2 Cu 3 O 8+ δ (x=0.25, 0.50, 0.75; denoted as Hg, Tl-1223), have been synthesized. All the diffraction lines of the samples were well indexed on the tetragonal “1223” (space group: P4/mmm) structure. X-ray powder diffraction data and EPMA results suggest that the compounds form complete ranges of solid solution. The superconducting transition temperatures for the as-synthesized samples are at about 124 to 128 K. After annealing in an argon atmosphere at 400°C for 6 h, the T c's of the samples with x=0.25 and 0.50 have been found to increase to 132 K. The Tl substituted compounds are quite stable up to 550°C whereas pristine HgBa 2(Ca 0.86Sr 0.14) 2Cu 3O 8+δ starts to decompose below 300°C. The intra-grain critical current density of Hg, Tl-1223 largely enhances as the thallium content increases. The Tl in Hg, Tl-1223 plays significant roles not only to stabilize the Hg-1223 phase but also to enhance the pinning properties.