Comparative study of J c-H characteristics for silver-sheathed superconducting Bi(2:2:1:2) and Bi(2:2:2:3) tapes

Abstract

Critical current densities J_c of silver sheathed Bi₂Sr₂CaCu₂O₈ and Bi₂Sr₂Ca₂Cu₃O₁₀ composite tapes fabricated by a partial melt and a powder‐in‐tube process, respectively, were measured at 4.2, 27, and 64 K as a function of applied magnetic field and the angle between the tape face and the direction of applied magnetic field. These measurements indicate that (1) the fraction of the grain boundaries, which are strongly coupled, are greater in the Bi(2:2:1:2)/Ag tapes than in the Bi(2:2:2:3)/Ag tapes; (2) the alignment of the Bi cuprate platelets with the c‐axis perpendicular to the tape face is significantly greater for the Bi(2:2:1:2) than for the Bi(2:2:2:3)/Ag tapes; and (3) the E‐J curves for both kinds of the tapes are described well by an expression, E∼exp[−(J₀/J)^μ], where μ and J₀ are constants below their transition magnetic fields H^*_g.