Microstructure and superconducting properties of bulk EuBCO-Ag with and without holes

Abstract

Bulk single-grain EuBCO-Ag superconductors with holes and without holes grown using a top-seeded melt-grow process are analysed. It turns out that the levitation force and the trapped magnetic field at 77 K are higher for the sample with holes (0,85 N and 1 T for the sample with a diameter of 28 mm and a height of 10 mm). Careful complex microstructural analyses undertaken by polarised light optical microscopy and scanning electron microscopy show that the reason for this behaviour is mainly the lower porosity of the sample with holes and the lower density of the of a/c-oxygenation cracks in non-porous areas along the holes. It also appears that other microstructural features, such as higher volume fraction of Eu2BaCuO5 particles in the a-growth sector than in the c-growth sector, uniform distribution of Ag particles in samples, presence of tetragonal EuBa2Cu3O7−x regions are similar on both types of samples and cannot significantly affect macroscopic superconducting properties. The influence of porosity on the local critical current density and transition temperature is also illustrated.