Isotropic round-wire multifilament cuprate superconductor for generation of magnetic fields above 30 T

Abstract

Magnets are the principal market for superconductors, but making attractive conductors out of the high-temperature cuprate superconductors (HTSs) has proved difficult because of the presence of high-angle grain boundaries that are generally believed to lower the critical current density, J(c). To minimize such grain boundary obstacles, HTS conductors such as REBa2Cu3O(7-x) and (Bi, Pb)2Sr2Ca2Cu3O(10-x) are both made as tapes with a high aspect ratio and a large superconducting anisotropy. Here we report that Bi2Sr2CaCu2O(8-x) (Bi-2212) can be made in the much more desirable isotropic, round-wire, multifilament form that can be wound or cabled into arbitrary geometries and will be especially valuable for high-field NMR magnets beyond the present 1 GHz proton resonance limit of Nb3Sn technology. An appealing attribute of this Bi-2212 conductor is that, being without macroscopic texture, it contains many high-angle grain boundaries but nevertheless attains a very high J(c) of 2,500 A mm(-2) at 20 T and 4.2 K. The large potential of the conductor has been demonstrated by building a small coil that generated almost 2.6 T in a 31 T background field. This demonstration that grain boundary limits to high Jc can be practically overcome underlines the value of a renewed focus on grain boundary properties in non-ideal geometries.

Strongly enhanced vortex pinning from 4 to 77 K in magnetic fields up to 31 T in 15 mol.% Zr-added (Gd, Y)-Ba-Cu-O superconducting tapes

“…We ascribe the excellent pinning performance at high temperatures to the high density (equivalent vortex matching field ∼7 T) of self-assembled BZO nanorods, while the low temperature pinning force is enhanced by large additional pinning which we ascribe to strain-induced point defects induced in the REBCO matrix by the BZO nanorods. Our results suggest even more room for further performance enhancement of commercial REBCO coated conductors and point the way to REBCO coil applications at liquid nitrogen temperatures since the critical current density J c (H//c) characteristic at 77 K are now almost identical to those of fully optimized Nb-Ti at 4 Thanks to its high critical temperature T c , high critical current density J c , high irreversibility field H irr , and moderate anisotropy parameter γ , REBa 2 Cu 3 O x (REBCO, where RE = rare earth) thin films grown on flexible and mechanically strong substrates can exceed the temperature and field application limits of the Nb-based low temperature superconductors, and enable superconducting applications in a broad temperature and magnetic field regime now exceeding 35 T at 4 K. [1][2][3] However, further J c and H irr enhancement and anisotropy reduction are strongly desirable for compelling, costeffective applications, and especially to enable multi-Tesla fields in a temperature regime of 30-77 K. [4][5][6] Enhanced vortex pinning is needed both to raise higher temperature irreversibility fields and to raise J c so that overall conductor current density J E can reach the required high values of the order of 500 A/mm 2 . Adding higher densities of nanoscale defects with strong vortex pinning properties is the most efficient strategy.…”

On the Mechanism of Cuprate Crystal Growth: The Role of Mixed Metal Carbonates

“…This is substantiated by considering the CaCO 3 /CaO/CO 2 equilibrium at elevated temperatures. While a melting temperature of T m = 1619 °C is given for calcite, this is unrealistic in an open reaction environment, given the propensity for CaCO 3 to decompose to CaO while liberating CO 2 . In an open system, effl uence of CO 2 away from the reaction shifts the equilibrium towards the oxide product, fi nally depleting the system of CaCO 3 .…”

“…[ 1 ] Several promising families of HTS materials exist, and among these, the rare-earth based R -123 family (so-called "second generation" HTS) is presently the leading candidate for widespread application. However, in the face of strong industrial demand for an isotropic, round-wire conductor, recent work [ 2 ] on the processing of Bi 2 Sr 2 CaCu 2 O 8+ x (Bi-2212) has yielded a signifi cant improvement in materials performance that has provided a second contender. Nonetheless, there are still diffi culties in the synthesis of phase-pure product in a scalable manner.…”

Improvement in granularity of NdFeAsO0.8F0.2 superconductor through Agx doping (x = 0.0–0.3)

“…As far as the improving of grain boundaries connectivity is concerned, a lot of work has already been done in case of cuprate superconductors and the addition of Ag has proven to be very effective [22][23][24][25][26]. Infact, to draw wires/tapes of high T c cuprates for their practical applications, researchers have drawn silver sheathed wires and tapes of them for their high current applications [27][28][29].…”

“…Infact, to draw wires/tapes of high T c cuprates for their practical applications, researchers have drawn silver sheathed wires and tapes of them for their high current applications [27][28][29]. It is known that Ag does not have any deteriorating effect on superconductivity of HTSc cuprates, primarily because Ag gets distributed at the grain boundaries instead of being substituted in the parent superconducting unit cell of these compounds [22][23][24][25][26][27][28][29]. This way Silver addition has resulted in improving the critical current of high Tc cuprates in a big way.…”