Weibull analysis of the electromechanical behavior of AgMg sheathed Bi2Sr2CaCu2O8 +xround wires and YBa2Cu3O7 − δcoated conductors

The development of superconducting magnets requires not only a conductor that is capable of carrying sufficient critical current density (Jc) at high magnetic field, but also one that is mechanically robust and predictable. Here, the electromechanical behavior of AgMg sheathed Bi2Sr2CaCu2O8 + x (Bi2212) round wires and YBa2Cu3O7 − δ (YBCO) coated conductors is studied using a statistical approach based upon three-parameter Weibull statistics, where the three parameters α, β, and γ describe the scale, shape and location of the resulting distribution function. The results show that Bi2212 round wire has significantly different behavior than previously studied Bi2212 tape conductors, with evidence of an underlying mechanically strong but poorly connected electrical 'backbone' in the round wire that is not found in the tape conductor. Furthermore, the Bi2212 round wire results indicate a distribution in the dependence of critical current upon strain (Ic(ε)) at the microscopic level, consistent with reports that a complex network of interfilamentary bridges plays a key role in connectivity. Unlike the behavior of either Bi2212 round wire or tape, the YBCO coated conductor shows a universal behavior for strains below yield, consistent with the presence of a strong, stiff NiW substrate that dominates the mechanical behavior, and a high purity, high density, highly textured YBCO layer with reversible electromechanical properties.