High-pressure oxygenation of thin-wall YBCO single-domain samples

Flux pinning in Al doped TSMG YBCO bulk superconductors

“…The first was standard oxygenation (SO), where the samples were slowly heated in a tubular furnace to 800 • C in a flowing O 2 atmosphere, kept there for 2 h, then slowly cooled to 400 • C and annealed there for 240 h. After annealing they were furnace cooled to room temperature. The second method of oxygenation was high pressure oxygenation (HPO), where the samples were oxygenated in a special high pressure vessel under an oxygen pressure of 16 MPa at 750 • C for 24 h with progressively increasing oxygen pressure [18], in order to avoid intensive cracking during oxygenation (for more information see [15]).…”

The influence of post-growth thermal treatments on the critical current density of TSMG YBCO bulk superconductors

“…The question is how we may eliminate the formation of these oxygenation cracks and at the same time keep a short oxygenation time. The oxygen diffusion rate can be significantly increased at higher oxygenation temperature, and high enough equilibrium oxygen content in YBa 2 Cu 3 O 7−x can be reached by higher oxygen pressure [8]. At the same time, the oxygen gap between the surface oxygenated layer and the core tetragonal phase must be kept lower than the critical one for crack formation.…”

Improved trapped field performance of single grain Y‐Ba‐Cu‐O bulk superconductors containing artificial holes

“…An established technique to address the issue of high porosity is to fabricate single grains containing an array of artificial columnar holes patterned into the pellets of pressed precursor powder. 5,[8][9][10][11][12] This is sometimes referred to as the "thin-wall" geometry. The artificial holes, typically each around 1 mm in diameter, then provide shortened paths for gas to escape from the sample microstructure during melt processing, resulting in reduced porosity within the superconducting matrix.…”

“…On the contrary, some perforated single grain samples have exhibited higher trapped magnetic fields than hole-free samples. 12 YBCO single grains processed with artificial holes have attracted attention recently from commercial suppliers of (RE)BCO bulk superconductors. 15,16 These samples were considered for superconducting bearing applications, in particular, where the use of bulk single grains enables high efficiency and reduces significantly contact, wear, and frictional losses.…”

“…In addition to reduced porosity, the benefits associated with the thinwall geometry also include, first, an increase in the specific surface area of the samples, which allows for more homogeneous and improved cooling that can be useful in preventing flux jumps 1,13 ; second, a decrease in the effective wall thickness, which assists with a more rapid and homogeneous oxygenation of the samples; and third, bulk microstructure almost free of oxygenation cracks along the ab-planes have been reported in thin-wall YBCO when processing was coupled with progressive oxygenation. 14 Melt processing bulk samples with artificial holes is a straightforward technique to implement, since it requires only one step to be added to the standard top-seeded melt growth (TSMG) fabrication process, namely the patterning of the artificial holes in the green body preform. Furthermore, it has been shown that samples grown with artificial holes do not suffer degradation in superconducting properties.…”