A new mercury-based superconductor with A T c of 132 K [Hg 0.5Tl 0.5Ba 2(Ca 1−xSr x) 2Cu 3O 8+ δ

Abstract

A new mercury-based superconductor Hg 0.5Tl 0.5Ba 2(Ca 1−xSr x) 2Cu 3O 8+ δ ) (x=0.14, denoted as Hg,Tl-1223) was prepared by solid state reaction of HgO, Tl 2O 3, Ba 2CuO 3+x, and Ca 1−xSr xCuO 2. X-ray powder diffraction analysis revealed that the Hg,Tl-1223 is isostructural with pristine HgBa 2(Ca 1−xSr x) 2Cu 3O 8+ δ . The crystal symmetry is tetragonal with a space group of P4/mmm, and lattice parameters of a = 3.8649(1) A ̊ and c = 15.9573(2) A ̊ . The T c for the as-synthesized sample is about 128 K. After annealing the sample in an argon atmosphere at 400 δC for 6 h, the T c has been found to increase to 132 K. In contrast to other mercury-based superconductors, HgBa 2Ca n−1Cu nO 2n+2+ δ (n=1, 2, 3), the Hg,Tl-1223 compound is quite stable even at 500 °C in oxygen and argon atmospheres. The Tl substitution at the Hg site appeares to stabilize the Hg,Tl-1223 phase and enhance pinning. The critical current density of the Hg,Tl-1223 obtained from the magnetic hysteresis loops is approximately twice larger than that of pristine HgBa 2(Ca 1−xSr x) 2Cu 3O 8+ δ .