Effects of Bi and Si substitutions on (Tl0.5Bi0.5-xSix)Sr2CaCu2O7 superconductor

Abstract

The effects of Bi and Si substitutions on the superconducting properties of (T10.5Bi0.5-xSix)Sr2CaCu2O7 (Tl-1212) for x = 0 to 0.5 were studied. The samples were prepared by the solid-state reaction method. X-ray diffraction patterns showed that lower substitution (x ≤ 0.2) of Si did not affect the formation of Tl-1212 phase. The temperature-dependent electrical resistance measurements showed that the onset transition temperature, Tc-onset and zero transition temperature, Tc-zero for x = 0–0.4 samples was between 91 and 96 K, and 78 and 81 K, respectively. AC susceptibility measurements showed transition temperature, Tcχ’ between 82 and 90 K. The peak temperature, Tp of the imaginary part of the susceptibility, χ” shifted to higher temperatures for x = 0 to 0.3 indicating enhancement of flux pinning and intergranular coupling. Further substitution of Si (x = 0.5) destroyed superconductivity of the Tl-1212 phase demonstrating that although Si can fully substitute Bi at Tl site and form majority (60%) Tl-1212 phase, superconductivity was not achieved. This work showed that Si could act as flux pinning centers for Tl-1212 high-temperature superconductor for low-level substitutions.