Towards high degree of c-axis orientation in MgB₂ bulks

The paper presents fabrication and characterization of spark plasma sintered textured (001) MgB₂ 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) MgB₂. 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 MgB₂ texturing as a novel and viable strategy for development of bulk MgB₂ with enhanced properties when taking advantage of its anisotropy.