On the influence of magnetic field processing on the texture, phase assemblage and properties of low aspect ratio Bi₂Sr₂CaCu₂O_x/AgMg wire

Abstract

Bi 2 Sr 2 CaCu 2 O x /AgMg conductors are potentially important for many applications up to 20 K, including magnets for cryogen-free magnetic resonance imaging and high field nuclear magnetic resonance research. One promising approach to increased critical current density is partial-melt processing in the presence of a magnetic field which has been shown to enhance c-axis texturing of wide, thin tape conductors. Here, we report on low aspect ratio rectangular conductors processed in an 8 T magnetic field. The magnetic field is applied during different stages of the heat treatment process. The conductors are electrically characterized using four-point critical current measurements as a function of magnetic field and magnetic field orientation relative to the conductor. The superconductive transition and magnetization hysteresis are measured using a SQUID magnetometer. The microstructures are characterized using scanning electron microscopy and energy dispersive spectroscopy and analyzed using digital image processing. It is found that the presence of a magnetic field during split melt processing enhances the electrical transport and magnetic behavior, but that the anisotropy is not consistently affected. The magnetic field also affects development of interfilamentary Bi2212 bridges, and that this depends on the initial shape of the Bi2212 filament. At least two behaviors are identified; one impacts the oxide phase assemblage and the other impacts textured growth.

Two-dimensional peridynamic simulation of the effect of defects on the mechanical behavior of Bi2Sr2CaCu2Oxround wires

“…Another important feature in Bi2212 RW microstructures is interfilamentary bridges connecting neighboring Bi2212 filaments. Studies of non-densified wires have shown that two types of bridges exist within Bi2212 RWs, smaller bridges (<2 μm) that are the result of outgrowths from one filament reaching another and which do not enhance transport, and larger bridges (2-4 μm in width) which play a key role in facilitating long-range transport in Bi2212 RWs by providing superconducting pathways for electron transport that bypasses defects [6,9,10]. In high J c densified wires, in which there is less porosity to bypass within the filaments, the role of interfilamentary bridges may be less significant.…”

“…The resolidification from the peritectic melt results in a heterogeneous microstructure; in addition to the desired Bi2212 phase, porosity and a variety of other phases, including Bi 2 Sr 2 CuO z (Bi2201), alkaline earth cuprates (AEC) and copper-free phases [8], are present in fullyprocessed wires. Furthermore, during resolidification, Bi2212 grains penetrate the Ag matrix, resulting in 'outgrowths' and interfilamentary bridges [9,10]. Figure 1(b) shows a crosssectional scanning electron microscopy (SEM) image of a fully-processed wire, illustrating the heterogeneous microstructure.…”

Magnetic Texturing of High-Tc Superconductors

“…Magnetic texturing of Ag-sheathed tapes was studied in very high fields and lead to high critical current densities [27,[29][30][31][32]. E. Flahaut demonstrated in his PhD the possibility to texture highly homogeneous Bi2212 tapes by moving the tape in the furnace and using a continuous melting process with large critical currents (Jc = 230kA/cm 2 at 4.2K, self field) [33].…”

On the role of a tape’s aspect ratio in the hysteresis losses of round superconducting cables

“…Additionally, all these conductors offer a wide variety of aspect ratios. When MgB 2based and Bi-based tapes have α up to few tens [29,35,36], YBCO conductors typically have α of several thousands, but on introducing striations, α can decrease to around 100 [37].…”