Towards high degree of c-axis orientation in MgB2 bulks

Abstract

The paper presents fabrication and characterization of spark plasma sintered textured (001) MgB 2 with a record degree of orientation of about 40% and 16% by high-energy ultra-sonication and slip casting in high magnetic field (12 T) and 0 T magnetic field, respectively. Structural characterization was performed by X-ray diffraction, and electron microscopy. The analysis revealed unexpected preferred orientation also in the MgO secondary phase due to the epitaxial growth of (111) MgO on (001) MgB 2 . The influence of oriented microstructure on the superconducting characteristics expressed by critical current density ( J c ), irreversibility field ( H irr ), and on the pinning properties were assessed. High anisotropy versus sample orientation in applied magnetic field, H , was observed for J c , H irr , pinning activation energy ( U *) extracted from relaxation measurements. The zero-field critical current, J c0 and F p,max are weakly or not dependent on the direction of H , while the other indicated parameters are significantly influenced. Results enable control of superconducting parameters by further optimization of microstructure through MgB 2 texturing as a novel and viable strategy for development of bulk MgB 2 with enhanced properties when taking advantage of its anisotropy.