High Tc Phase of Bi-Sr-Ca-Cu-O Superconductor

Abstract

High T _c superconducting phase above 100 K in a Bi-Sr-Ca-Cu-O superconductor was found to appear in proportion to the time of the sintering just below the melting temperature. The changes of the magnetic susceptibility for this high T _c phase corresponded well to the behavior of 4.8° peak in X-ray diffraction pattern taken with Cu-K_α, which indicated that the high T _c phase contains triple Cu-O layers sandwiched by two Bi₂O₂ layers. The mechanism of the high T _c phase formation is proposed such that a disproportionation into triple and single Cu-O layers occurs from 80 K phase with double Cu-O layers to form the high T _c and a semiconducting phase, respectively.