Fabrication and characterization of large Nd–Ba–Cu–O grains prepared under low oxygen pressure

Abstract

A large, single-grain Nd-Ba-Cu-O (NdBCO) composite consisting of superconducting NdBa 2 Cu 3 O 7−␦ containing nonsuperconducting Nd 4 Ba 2 Cu 2 O 10 phase inclusions was fabricated up to 2 cm in diameter using a top-seeded melt-textured growth technique. A MgO single-crystal seed was used to provide a heterogeneous nucleation site at the center of a presintered pellet heated above its peritectic temperature and cooled continuously in a conventional tube furnace in reduced oxygen partial pressure. This process produces individual grains with the c axis oriented at ≈10°to the seed surface which, from vibrating-sample magnetization measurements, exhibit a pronounced peak effect in their magnetic moment over a wide temperature range (50-90 K) when the supercurrent flows in the a-b planes. A very high irreversibility field (>9 T at 77 K) is also observed in these grains for field applied both perpendicular and parallel to the crystallographic c axis which is significantly greater than that observed in good-quality melt-processed Y-Ba-Cu-O. These results underline the potential of NdBCO for high-field engineering applications.

Recent progress in large-grain REBCO melt texturing

“…Cooling from the peritectic state in p(O 2 ) ≈ 0.1% naturally promotes the formation of a low substitution phase, resulting in a high critical-transition temperature (T c ≈ 95 K). 13,46 Alternatively, NdBCO grains grown under higher p(O 2 ) can also have a similar T c after annealing in argon at 900-980°C and oxygenation at ∼350°C. 39,40 Another advantage of growing these REBCO grains under low p(O 2 ) is the formation of a spatially modulated RE 3+ -Ba 2+ substitution level on the nanometer scale.…”

“…7,8 When they are processed in bar shapes, they also form the critical parts of fault current limiters 9,10 and current leads. 11,12 All of these applications make use of the ability of these materials to sustain critical current densities (J c s) of 10 4 -10 5 A/cm 2 at 77 K under external magnetic fields of 0-3 T, [13][14][15] as well as the feasibility of producing these materials reproducibly in large batches. 16 At this point, large-grain yttrium-barium-copper-oxide (YBCO) materials fulfilling these requirements are already available commercially.…”

Effect of Corrosion Inhibitor, Benzotriazole, in Cu Slurry on Cu Polishing

“…Some groups have overcome this difficulty by using a hot, NdBCO self-seeding technique to obtain large single grains with their c-axes oriented perpendicular to the sample surface [4]. MgO has been used to seed large NdBCO grains although the c-axis typically lies parallel to the top surface of the pellet in these samples, which is not favourable for generating large magnetic fields [5].…”

Optimization of seeding conditions for the fabrication of c-axis-oriented large NdBCO–Ag grains

“…In comparison to YBCO, NdBCO has higher superconducting transition temperature (T c , about 95 K), 11,12 higher irreversibility fields (about double that of YBCO at 77 K) [12][13][14] and a more prominent J c peak effect. 10,12,15 These superconducting properties, as originated from both electronic structures and the spatially modulated substitution of Ba onto the Nd sites on a nanometer scale, [16][17][18] can enable such materials to be used in high magnetic fields. In addition to these properties, the growth rate of NdBCO grains has also been shown to be about one order of magnitude higher than that of YBCO, 19 which is normally around 0.5 mm/h under a low-temperature gradient environment.…”

“…The melting point of NdBCO, however, is the highest in the REBCO family [about 1353 K 25 in air and 1308-1313 K when p(O 2 ) ‫ס‬ 1% 25,26 ] so that the choice of seeds is practically limited to MgO single crystals, although the orientation of the grains derived from MgO is difficult to control. 12 Thus the goals of NdBCO processing cannot be achieved unless an alternative processing environment can be derived and appropriate seeds can be found. A partial solution to these problems has been demonstrated by Yoo et al, 11 Ikeda et al, 27 and Chauhan et al, 28 who grew Ag-doped NdBCO (NdBCO-Ag) large grains using NdBCO seeds at high temperature when NdBCO-Ag precursors were melted and undercooled.…”