The use of buffer pellets to pseudo hot seed (RE)–Ba–Cu–O–(Ag) single grain bulk superconductors

Abstract

Reliable seeding of the superconducting (RE)Ba 2 Cu 3 O 7−δ (RE-123) phase is a critical step in the melt growth of large, single grain, (RE)BaCuO ((RE)BCO) bulk superconductors. Recent improvements to the top seeded melt growth (TSMG) processing technique, which is an established method of fabricating bulk (RE)BCO superconductors, based on the use of a buffer layer between the seed and green body preform, has significantly improved the reliability of the single grain growth process. This technique has been used successfully for the primary TSMG and infiltration melt growth of all compositions within the ((RE)BCO-Ag) family of materials (where RE=Sm, Gd and Y), and in recycling processes. However, the mechanism behind the improved reliability of the melt process is not understood fully and its effect on the superconducting properties of the fully processed single grains is not clear. In this paper, we investigate the effect of the use of a buffer pellet between the seed and green body on the microstructure, critical current, critical temperature and trapped field of the bulk superconductor. We conclude that the introduction of the buffer pellet evolves the melt growth process towards that observed in the technologically challenging hot seeding technique, but has the potential to yield high quality single grain samples but by a commercially viable melt process.

Reliable 4.8 T trapped magnetic fields in Gd–Ba–Cu–O bulk superconductors using pulsed field magnetization

“…In the experiment, a 36 mm diameter GdBCO-Ag sample, as shown in figure 1(a), was selected from a batch of melt textured samples prepared using the standard top-seeded melt growth process [28]. Its peak trapped field, magnetized by FC at liquid nitrogen temperature, was 1.2 T. Our state-of-the-art processing technique is able to maintain performance to a sample diameter of over 50 mm [29].…”

Pulsed Field Magnetization of Single-Grain Bulk YBCO Processed From Graded Precursor Powders

“…For this study, a graded, single grain YBCO sample was fabricated using a buffer-aided, top-seeded melt-growth (TSMG) process [11]- [13]. Two layers of precursor powders were arranged in U-shaped stacks, as shown in Fig.…”

“…Precursor powders containing 70 wt% Y-123 + 30 wt% Y-211 were used for both stacks, with 2 wt% CeO 2 added in the top region (close to the seed/buffer) and 1 wt% CeO 2 in the bottom region [11]. A buffer pellet is used improve the success rate of the melt-growth process and to aid the growth of the Y-123 phase for improved superconducting properties [12], [13]. The as-grown, pre-polished sample and the sample after polishing and mounting for magnetization experiments are shown in Fig.…”

A portable magnetic field of >3 T generated by the flux jump assisted, pulsed field magnetization of bulk superconductors

“…Figure 1(a) shows the portable magnet system. A 30 mm diameter, 12 mm thickness GdBCO bulk, single grain superconductor prepared via the conventional top seeded melt-growth (TSMG) technique [21] was installed in a copper sample holder located at the top of the vacuum can. Slots were made in the copper holder to reduce the formation of eddy currents during magnetization, as shown in figure 1(b).…”