Relationship between local microstructure and superconducting properties of commercial YBa₂Cu₃O_7−δ bulk

Abstract

The relationship between local microstructure and superconducting properties of commercially prepared YBa 2 Cu 3 O 7−δ single-grain bulk superconductor was investigated. The small samples for magnetization measurements were taken from the beginning and end of the a-growth sector and the c-growth sector as well as from the beginning and end of a/a-growth sector boundary. The field dependence of the magnetic moment was measured at temperatures starting from liquid helium (4.2 K) to liquid nitrogen (77 K) using the commercial Magnetic Property Measurement System with a magnetic field of up to 7 and 18 T. The microstructure was analysed using polarised light optical microscopy and scanning electron microscopy. The quantitative microstructural data were determined using an image processing software package. Microstructure analysis was focused on the size and volume fraction of Y 2 BaCuO 5 particles as well as on the characterisation of subgrain structure. These measurements showed that not only inhomogeneous distribution of Y 2 BaCuO 5 particles had influence on the critical current density but it can also be significantly affected by the subgrain structure within the bulk or by local contamination of YBa 2 Cu 3 O 7−δ from the seed during fabrication process. It was observed that the critical current density along the a/a-growth sector boundary could be substantially higher in comparison to the other parts of the bulk and this behaviour can be related to the subgrain structure in the sample.

Review on the Use of Superconducting Bulks for Magnetic Screening in Electrical Machines for Aircraft Applications

“…As expected, the YBaCuO bulk [45] exhibits properties close to a perfect diamagnet for magnetic fields as high as 2 T due to a critical current of 4500 A/mm 2 and starts to shows a tiny difference at 4 T where the critical current reached 5000 A/mm 2 . This increase of critical current is due to the well-known fishtail effect [46].…”

“…Even more problematic is the evolution of the superconducting properties along the sample radius as reported in several papers [57][58][59]. For example, Antal et al [45] present a diminuation of 24% of the J c of two samples distant of only 8 mm along the radius of a commercial YBaCuO bulk at 2 T and 4.2 K. Finally, for very large sample the homogeneity is even harder to achieve as it cannot be control during the preparation process, either during the synthesize or the machining, the consequence is the presence of weak parts where superconductivity is bad. This can be seen in Figure 13 where, for a large commercial ring segment-shaped GdBaCuO bulk, a weak area of superconductivity can be seen during a field cooling magnetization at 77 K. Another method for preparing large size single crystal is the so-called infiltrationgrowth technique.…”

Characterization of High-Temperature Superconductor Bulks for Electrical Machine Application

“…This means the determination of the critical current density J C . Different classical methods have been used for small samples [ 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 ]. The goal of these classical methods is mainly to obtain the dependence of J C on the magnetic field B and temperature of the HTS material.…”

“…Hence, for real HTS bulks used in electrical applications, other methods are necessary, allowing characterization of the entire HTS bulks without cutting. Recently, the CAN company [ 8 ], building and selling HTS YBaCuO bulks, proposed characterizing different samples of HTS material placed at different regions in the YBaCuO bulk to better characterize their products. This proves that companies need a characterization method for entire HTS bulk.…”

Efficient Fabrication of Ultralight YBa2Cu3O7−x Superconductors with Programmable Shape and Structure

“…Certain applications such as portable systems for medical devices, ultralight rotating machines for power applications, and superconducting filters with unique shapes require YBCO bulk of various shapes with low gravity and better processability. [ 16 ] The development of such a preparation method has been a long‐standing problem in the field of superconducting material fabrication.…”