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.

YBCO bulk single-grain samples with and without cerium oxide addition, were prepared by the two-step top seeded infiltration growth. The microstructure observations showed that cerium oxide addition led to formation of small Y 2 BaCuO 5 (Y211) particles in the YBa 2 Cu 3 O 7 singlegrain matix. On the other hand, the sample without cerium oxide addition exhibited clusters of large Y211 particles. Observed difference in Y211 paricles led to significantly different size of a/c-oxygenation cracks. While the mean length of a/c-cracks in the sample with cerium oxide addition was several hundred micrometers, it was smaller than 50 μm in the sample without cerium oxide addition. It was shown that the clusters of large Y211 particles can effectively prevent extension of oxygenation a/c-cracks. The trapped magnetic field measured at 77 K is shown.

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