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Single domain YBCO bulk superconductors were prepared using a conventional top-seeded melt growth (TSMG) technique. Artificial holes were introduced to the green sample prior to thermal processing using a bespoke "spiked" mould. Mechanical properties such as elastic modulus, Vickers hardness, compressive strength and tensile strength were measured and compared to the properties of a standard bulk. The presence of the holes the bulk microstructure was observed to limit porosity and lower the concentration of macro-cracks in the bulk microstructure, resulting in significantly enhanced mechanical properties of the bulk single grains. The elastic modulus of the perforated bulks was observed to exhibit an increase of more than 45% compared to the standard samples. Compressive and tensile strengths were also improved significantly in the samples containing artificial holes. Observed differences in Vickers hardness, on the other hand, were negligible. This could be due by the fact that the hardness is measured on a small surface area of the single grain sample, where the effect of lower porosity and lower concentration of macro-cracks is less relevant. The introduction of artificial holes to the bulk, single grain microstructure appears to be a very promising technology for the production of melt-textured bulk superconductors with enhanced mechanical properties.

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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.

Superconducting magnetic bearings are becoming more widespread, due to the unique properties they provide. Their efficiency is unparallel, there are no issues such as contact, friction, and wear. They require low or minimal maintenance, no lubrication and they work under extreme conditions (cryogenic temperatures, high vacuum). In this contribution, the influence of geometric properties of superconducting bulks on the performance of superconducting bearings was studied. The main focus was paid to load capacity, radial and axial stiffnesses. Two samples with a significantly higher aspect ratio compared to conventional bulks were prepared. One of these samples was synthesized with artificially created holes. The samples were prepared using top-seeded melt-growth process with an additional source of a liquid phase in the form of an underlaying pad. The original thickness of 16 mm of the samples with a diameter of 28 mm was repeatedly ground down. Levitation force and trapped field were measured after each grinding step. Using this approach, the dependence of properties of the bulks on their thickness, scaling of these properties with thickness and the influence that artificial holes can make on the properties of finished single domain bulks were studied. The maximum levitation force was greatly improved for bulks with thicknesses of 2-6 mm. Such data is of the utmost importance in the field of superconducting YBCO single domain bulk ceramics, as it allows for better understanding and further improvement of both the manufacturing process and real-world applications of these materials.