Superconducting properties and structural stability of Bi2Sr2CaCu2O8+δ compound prepared by electrochemical reduction in protogenic electrolyte

Abstract

Superconducting Bi2Sr2CaCu2O8+δ (Bi-2212) compound was electrochemically reduced in a protogenic electrolyte of benzoic acid dissolved in acetone. The critical temperatures (Tc) of the reduced Bi-2212 were enhanced from 75 K up to ∼90 K, which were reportedly the highest value of Bi-2212 superconductor. In spite of the enhancement of Tc, a diamagnetism of Bi-2212 was weakened after the reduction. This phenomenon was discussed in terms of the flux penetration depth. The electrochemically reduced Bi-2212 had a different structural stability from a partly oxygen-removed Bi-2212 which was prepared by annealing in reducing atmospheres. These results are attributable to injection of protons from the benzoic acid into the Bi-2212 structure.