The Processing and Properties of Bulk (Re)bco High Temperature Superconductors: Current Status and Future Perspectives

Abstract

Bulk (RE)-Ba-Cu-O [(RE)BCO] cuprate HTS have been developed steadily towards a wide range of sustainable engineering and technological applications since their discovery in 1986 based primarily on their unique potential to trap very large magnetic fields (>5 T) at temperatures that are accessible potentially by thermo-electric cooling techniques. Trapped fields of ∼10 T at the surface of individual (RE)BCO bulk single grains and in excess of 17 T in a reinforced two-sample stack are now being achieved reliably. This paper reviews the current state of the art of the processing of large, single grain (RE)BCO bulk superconductors required to trap fields of this magnitude, and specifically via two advanced fabrication approaches; the traditional TSMG process and the more recently developed TSIG technique. The focus of the review is on optimising the critical processing parameters to achieve high-quality, high performance single grain (RE)BCO bulk superconductors specifically for high-field applications. The review also summarises recent advances in processing, such as the integration of the so-called buffer technique into the TSMG and TSIG processing methodologies to achieve improved reliability in single grain growth with a success rate exceeding 90%, the development of a Mg-doped NdBCO generic seed crystal for the successful growth of all rare-earth and light-rare earth based bulk superconductors [(RE)BCO and (LRE)BCO] and the introduction of nano-size stable, non-superconducting phase(s) to the bulk microstructure to improve the intrinsic flux pinning strength of the material, and hence trapped magnetic field. Details of the two-step buffer-aided TSIG technique developed recently that yields dense, near-net shaped, high performance (RE)BCO bulk superconductors with improved superconducting and mechanical properties are also presented. Suitable sample-seed configurations for effective multi-seeding are discussed, which enables the production of high aspect ratio, bar-shaped (RE)BCO quasi-single grains that exhibit improved levitation forces required in Maglev-based applications, for example, are discussed. The electrical, mechanical, microstructural and magnetic properties (including those achieved from a pulsed-field magnetisation approach) of the different (RE)BCO systems are presented and the relevant correlation in properties and performance highlighted, accordingly. Finally, a brief summary of existing applications and prospects for near-future exploitation of these remarkable, technologically important materials, and particularly in the medical and pharma-industries, is provided.

Microstructural Parameters for Modelling of Superconducting Foams

“…This is illustrated in the temperature program shown in Figure 1 a. The green Y-211 foam (3) is then converted into the YBCO superconductor using the IG process [ 32 , 33 ] using a Nd-123 seed crystal on top and a liquid source consisting of a 1:1 mixture of Ba and Cu oxides with an overall stoichiometry of Ba Cu O and additional 123 powder placed beneath the Y-211 foam. When being heated above the eutectic temperature (1010 C, (4)), the liquid phase infiltrates the Y-211 foam by capillary action [ 36 ].…”

“…Although to a first approximation, the ceramic material will mimic the structural arrangement of the polymer foam. Furthermore, the infiltration growth (IG) process [ 32 , 33 ] applied to the foam sample will create a unique microstructure, which is not seen in bulk superconductors [ 34 ] due to the large amount of internal surfaces in the foam structure.…”

Microstructural Parameters for Modelling of Superconducting Foams

“…This is illustrated in the temperature program shown in Figure 1a. (ii) The green Y-211 foam (3) is then converted into the YBCO superconductor using the IG process [32,33] using a Nd-123 seed crystal on top and a liquid source consisting of a 1:1 mixture of Ba and Cu oxides with an overall stoichiometry of Ba 3 Cu 5 O y and additional 123 powder placed beneath the Y-211 foam. When being heated above the eutectic temperature (1010 • C, (4)), the liquid phase infiltrates the Y-211 foam by capillary action [36].…”

Microstructural Parameters for Modelling of Superconducting Foams

“…The already existing modelling approaches for polyurethane foams [20][21][22][23][24] may pro- the infiltration growth process [31,32] applied to the foam sample will create an unique 12 microstructure which is not seen in bulk superconductors [33] due to the large amount of In the following, a foam strut denotes an entire broken-out section and the ligament is 78 the material section between two adjacent nodes. In case of higher magnification (c,d),…”