Identification of the intermediate phase Bi4Sr4Ca3Cu5O18+δ during Bi/2212 and Bi/2223 conversion

Abstract

Among all the high-temperature superconductors, Bi/2223 is the most promising material as tapes and wires for large-scale and high-current applications. However, synthesizing Bi/2223 as a single phase is extremely difficult because of its relatively poor thermal stability and the narrow ranges of stoichiometry and temperature for its formation. Recently, to understand the formation mechanism and establish the optimum heat treatment conditions for the growth of Bi/2223, we have systematically studied phase transformation of the Bi-based superconductors. In this article, we report our finding of the intermediate phase of Bi4Sr4Ca3Cu5O18+δ (Bi/4435).Bi/2212 tapes with a Bi/2223 composition, produced by the standard “oxide powder in tube” process, were used in the study. TEM cross-section specimens were prepared from the bulk samples that were quenched or furnace-cooled from different stages during the Bi/2212 and Bi/2223 conversion.Figure 1 shows a lattice image of the Bi/4435 phase with an alternating narrowly and widely spaced lattice (each black line corresponds to the position of the BiO layer).