Growth-related microstructure of melt-grown REBa2Cu3Oy bulk superconductors

The solidification process introduces defects into melt-grown REBa2Cu3Oy (123) bulks, which then influence the overall superconducting and mechanical properties of the fabricated tiles. The most important microstructural features related to the growth process are the subgrain boundaries and the macroscopic inhomogeneity in the concentration of the RE2BaCuO5 (211) particles. It is shown, in this paper, that the growth of the 123 bulks in the growth sectors is responsible for the macroscopic arrangement of these defects in a sample. A mechanism of subgrain formation, which is based on the formation of dislocations during the engulfing of the 211 particles by the growth of the 123, is proposed. Macroscopic residual stresses caused by 211 macroscopic inhomogeneity are estimated. The change of the macroscopic sample shape is associated with the liquid transport from the slower a-axis growth front to the faster c-axis growth front at the edge between the a- and c-growth sectors.