Effects of Li doping on the superconducting properties of Bi-based superconducting whiskers

Abstract

The effects of Li doping on the superconductivity of Bi-based superconducting whiskers have been investigated. The Li doping is effective in increasing T c of both the Bi 2Sr 2CaCu 2O x (2223) whiskers. The Li-doped 2212 whiskers show a T c at 82 K, which is higher than that of the undoped 2212 whiskers by 5 K. The Li-doped and undoped 2223 whiskers have been prepared by the Conversion by Annealing in Powder (CAP) method. An enhancement of T c by 1.2 K is achieved by Li doping of the 2223 whiskers. The T c of the 2223 phase is commonly accepted to be lowered by a reduction of hole concentration, which is opposite to the situation of the 2212 phase. Therefore, the mechanism of the enhancement of T c is not due to the optimization of the hole concentration. From the compositional analysis and the measurement of the c-axis lattice parameter, the Li doping is thought to be effective in increasing the Sr/Ca ratio for both kinds of whiskers, which causes the enhancement of T c.