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Relationship between local microstructure and superconducting properties of commercial YBa2Cu3O7−δ bulk

The relationship between local microstructure and superconducting properties of commercially prepared YBa2Cu3O7−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 Y2BaCuO5 particles as well as on the characterisation of subgrain structure. These measurements showed that not only inhomogeneous distribution of Y2BaCuO5 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 YBa2Cu3O7−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.