Comprehensive Microstructural Study of 35 mm GdBCO/Ag Bulks Grown by SDMG

The recently developed SDMG exhibits impressive superconducting properties in prepared bulks, as reported in the literature. However, a comprehensive study of its microstructural properties, particularly in larger industrially produced bulks, has not yet been published. It has been generally assumed that the microstructure of SDMG-grown bulks is comparable with other melt-processed bulks, with the exception of distribution in the a -axis, which seems quite reasonable given the monodirectional seeding approach. The microstructure of the 35 mm GdBCO/Ag bulk was studied in detail. The results show extraordinary improvements in homogeneity across the a -axis in green phase, silver and porosity distributions. These improvements are attributed to be a direct consequence of the SDMG growth mechanism, in which growth proceeds exclusively in the c -direction, eliminating the ab -growth front and resulting in more uniform inclusion and porosity distributions in the ab -plane. The obtained results increase the confidence in the previously published microstructural data on small-diameter early samples, as well as provide information for further in-depth research of SDMG-grown bulks.