Among REBa2Cu3O7-δ (REBCO, RE=rare earth elements) superconductors, which are known for their high critical temperature (Tc), GdBCO is superior due to its formation of low-proportion of solid solutions of lower Tc and resulting large critical current densities (Jc). Bulk single grain superconductors are interesting for various applications such as generating tesla-scale homogeneous magnetic fields useful for motors and various medical fields, levitation platforms, vibration dampers, etc. In this study, we focused on growth of bulk single grains of GdBCO by top-seeded melt growth technic by the addition of 30 wt.% of nano-meter sized, sharp-edged Gd2BaCuO5 (Gd211) particles produced via employing high-energy ultrasonication (450 W for 30 min, GdBCO-Ultra). The comparison of the isothermal growth studies performed at several sintering temperatures on the GdBCO bulks with conventional and sharp-edged Gd211 particles indicated that later showed faster growth rates and effective peritectic reaction. Microstructural properties investigated by the scanning electron microscopy indicated two types of Gd211 particles in the GdBCO bulk sample, one that was larger sized essentially produced by melting of the Gd123 phase and another are fine sized by the ultrasonically added. Homogeneous dispersion of fine sized (about 100 nm) non-superconducting Gd211 particles in the matrix of GdBCO-Ultra samples was observed. As a result of higher interfacial defect density along with reduced macro-porosity, improved the self-field Jc of GdBCO-Ultra from 44.5 kA/cm2 to 125 kA/cm2 at 77 K. It should be noted here that without addition of economically costly grain refining agents, fine sized 211 phase was obtained in the bulk GdBCO single grain. Addition of dopants may further improve the properties of GdBCO-Ultra superconductors as strong superconducting magnets for high-field applications.
Keywords: GdBa2Cu3O7-δ single grain, Ultrasonic irradiation, Microstructure , Critical current density