Microstructure of DyBCO bulk superconductors prepared using single-direction melt-growth (SDMG) method

Abstract

The microstructure of DyBCO bulk single grain superconductors (BSS) with a nominal composition of 7 mol DyBa2Cu3Oy + 3 mol Dy2BaCuO5 (Dy211) + 10 wt % Ag2O + 0.5 wt % CeO2 prepared by single-direction melt-growth (SDMG) was studied using electron and optical microscopy. Microstructural parameters such as subgrain structure, porosity, size and macroscopic distribution of Dy211 particles, interdiffusion of the Eu from the EuBCO seed, as well as the position of the remaining tetragonal non-oxygenated regions in the sample were characterized. The volume fraction of Dy211 particles increases with distance from the seed, which induces thermal mechanical stresses that are compressive at the seed side and tensile at the growth end with an estimated maximum of 110 MPa. Multinucleation on the large seed leads to the appearance of steps at the growth front and the formation of a-growth subsectors with a higher concentration of Dy211. A high concentration of Eu is diffused from the EuBCO seed in the first part of the samples. The diffusion depth is similar to that of YBCO BSS from a Yb-containing substrate.