Non-invasive 3D characterization by X-ray computer tomography of single-grain RE-Ba-Cu-O bulk superconductors

Bulk single-grain superconductors (BSS) (RE) 1.8 Ba 2.4 Cu 3.4 O x (RE = Y, Eu) added with CeO 2 and Ag 2 O in the case of Eu-BSS (diameter of 32 mm, thickness of 14 mm), with and without artificial columnar holes, grown using a top-seeded melt-growth process, were characterized by X-ray computer microtomography (XRCT). The presence of artificial columnar holes decreases total porosity and, in their proximity, porosity is lower. The influence of the holes is stronger in Y-BSS, and their impact on large and small pores depends on the material. The largest pores were found in Y-BSS. Eu-samples present a higher porosity and more uniform distribution than Y-samples. Hence, Eu- and Y- BSS behave in a different manner during growth. This influences geometrical perfection of artificial holes: a lower deviation from the ideal shape of a cylinder is accompanied by a higher uniformity of porosity in Eu than in Y samples. In Eu-BSS, T c is higher than in Y-BSS. Transitions are wider and more different (depending on top, middle, bottom locations) for Eu- than for Y- BSS, suggesting different oxygenation depending on material type and porosity details. Self-field J c (0) is higher for Y samples. At high fields, J c is superior in Y samples at 50 K, while at 77 K it equals or is below the values for Eu samples. Work demonstrates unique possibilities and increased prospects of the 3D XRCT use over 2D traditional microscopy techniques. Its development and integration with production, better understanding of limitations and further improvements will benefit the quality and application of BSS.