Dependence of T_c and the Crystal Structure of Tl_2-zBa₂Ca_1.95Y_0.05Cu₃O_y Superconucting Oxide on the Tl

Abstract

Superconductors, Tl_2-zBa₂Ca_1.95Y_0.05Cu₃O_y, with variable Tl contents were prepared. We investigated the dependence of their properties, crystal structures and T_c on the Tl content. The Cu valence decreased with decreasing Tl content, 2-z, in the region of 2-z≥1.5 but increased in the region of 1.2≤2-z<1.5. The critical temperature, T_c changed with decreasing Tl content. T_c(zero) was 116 K at 2-z=1.7. When the Tl content was decreased, T_c(zero) reached the maximum value of 119 K at 2-z=1.2. The results of structure refinements of samples with different Tl contents with neutron powder diffraction data show that Cul-Ca, Y and Cu2-Ca, Y lengths had the largest and smallest values at 2-z=1.5. At this Tl content, T_c(zero) was the lowest of 108 K, and copper-apical oxygen (Cu2-O3) bond length was the smallest.