Factors Affecting the Growth of Multiseeded Superconducting Single Grains

Abstract

Single grain, rare earth-barium-copper oxide [(RE)BCO] bulk superconductors, fabricated either individually or assembled in large or complicated geometries, have significant potential for a variety of potential engineering applications. Unfortunately, (RE)BCO single grains have intrinsically very low growth rates, which limits the sample size that may be achieved in a practical, top seeded melt growth (TSMG) process. As a result, a melt process based on the use of two or more seeds (so-called multi-seeding) to control the nucleation and subsequent growth of bulk (RE)BCO superconductors has been developed to fabricate larger samples and to reduce the time taken for the melt process. However, the formation of regions that contain non-superconducting phases at grain boundaries has emerged as an unavoidable consequence of this process. This leads to the multi-seeded sample behaving as if it is composed of multiple, singly seeded regions. In this work we have examined the factors that lead to the accumulation of non-superconducting phases at grain boundaries in multi-seeded (RE)BCO bulk samples. We have studied the microstructure and superconducting properties of a number of samples fabricated by the multi seeded process to explore how the severity of this problem can be reduced significantly, if not eliminated completely. We conclude that, by employing the techniques described, multi-seeding is a practical approach to the processing of large high performance superconducting bulk samples for engineering applications.

Production of Sharp-Edged and Surface-Damaged Y2BaCuO5 by Ultrasound: Significant Improvement of Superconducting Performance of Infiltration Growth-Processed YBa2Cu3O7−δ Bulk Superconductors

“…Among, non-superconducting and non-interacting inclusions such as the 211 phase, particles are considered as effective pinning centers. The defect density due to the left back 211/123 interfaces will be of coherence length size and effectively pins the fluxons and aids in improving the J c performance of the single-grain REBCO bulk products. − …”

Pulsed Field Magnetization of Bridge-Seeded Bulk YBCO Using Solenoid and Split Coils

“…The as-grown single grain was then cut into a slice of length 10 mm, parallel to the a direction of the crystallographic lattice, which was then machined into a bridge-shaped seed and used to multi-seed the bulk YBCO sample based on controlled alignment and relative orientation of the two legs of the seed (0°-0°) [4]. Special care was paid to the alignment of the seeds [10] by selecting a better bridge seed by visual examination, as commonly carried out when selecting single seeds for normal TSMG.…”

Fabrication of high-quality joints between Gd–Ba–Cu–O bulk superconductors

“…The trapped magnetic fields (RE)BCO bulk superconductors can achieve are significantly larger than those achieved by conventional magnets [1,[6][7][8][9]. Growth of samples larger than 30 mm in diameter has, however, generally led to a deterioration of superconducting properties as well as reduced mechanical strength and inhomogeneous penetration of oxygen during post-growth oxygenation [5,10].…”