Design and characterisation of ex situ bulk MgB<sub>2</sub> superconductors containing a nanoscale dispersion of artificial pinning centres
Guillaume Matthews, Junliang Liu, C.R.M. Grovenor, Patrick S. Grant, Susannah Speller
Abstract
Abstract MgB 2 pellets containing a nanoscale dispersion of artificial pinning centres have been successfully manufactured through a powder metallurgy route based on the oxide dispersion strengthened (ODS) concept more usually used for steels and superalloys. Commercial MgB 2 powder and Y 2 O 3 nano-powder were mechanically alloyed in a high energy planetary ball mill and consolidated using the field assisted sintering technique. The composite powders were ball milled for different times up to 12 h and characterised by means of particle size analysis, x-ray diffraction (XRD) and scanning transmission electron microscopy (STEM). The microstructure and superconducting properties were characterised by density, XRD, STEM and magnetic property measurements. The powder microstructure comprised Y 2 O 3 particles dissolved into the MgB 2 matrix. After consolidation there was a near-uniform dispersion of precipitated YB 4 and MgO particles. A bulk 0.5 wt% Y 2 O 3 -MgB 2 composite showed the best superconducting performance with a significant improvement in J c at high field compared with unmodified MgB 2 , and only a small reduction in T c . The results suggest that the ODS concept is promising to improve the superconducting properties of MgB 2 .