Tc Enhancement of Bi-based Superconductor by Liquid Phase Treatment

Abstract

A remarkable Tc enhancement of the Bi-based 2212 phase (Bi_1.8Pb_{0. 2}Sr₂Ca₁Cu₂O_y) was observed by liquid phase treatments under mild conditions. Soaking treatments in the solutions of polyhydric phenols such as hydroquinone were specially effective, and in those cases, the Tc values were increased by more than 10K by the treatments at room temperature. The solutions of metal iodides such as LiI were also effective to increase the Tc. In both cases, the increases of the Tc were presumed to be caused by the reductive actions of the treating solutions, which decreased and optimized the hole concentrations of the superconductors. In the case of hydroquinone treatment, increase in the c-axis length of the 2212 phase, which was larger than that in the case of inert gas treatment, was observed. Therefore, it was suggested that the organic compounds derived from hydroquinone were intercalated, partially, between some layers of the 2212 phase, but no other evidence was obtained. In the case of metal iodide treatment, strong adsorption of metal cations into the superconductor was observed, but details of the adsorption state and effects on the superconductivity were not clarified.