Combined addition of nano diamond and nano SiO2, an effective method to improve the in-field critical current density of MgB2 superconductor

Highlights: → Both nano diamond and nano SiO2 caused significant modifications in the structural properties of pure MgB2 sample. → Reduction in TC for the best codoped sample was approximately 2 K. → The best codoped sample yielded a JC, an order of magnitude more than the undoped one at 5 K and 8 T. → The enhanced flux pinning capability provided by the additives is responsible for the improved in-field JC. -- Abstract: MgB2 bulk samples added with nano SiO2 and/or nano diamond were prepared by powder-in-sealed-tube (PIST) method and the effects of addition on structural and superconducting properties were studied. X-ray diffraction (XRD) analysis revealed that the addition caused systematic reduction in 'a' lattice parameter due to the substitution of C atoms at B sites and the strain caused by reacted intragrain nano particles of Mg2Si as evinced by transmission electron microscope image. Scanning electron microscopy images showed distinct microstructural variations with SiO2/diamond addition. It was evident from DC magnetization measurements that the in-field critical current density [JC(H)] of doped samples did not fall drastically like the undoped sample. Among the doped samples the JC(H) of co-doped samples were significantly higher and the best co-doped sample yielded a JC, an order of magnitude more than the undoped one at 5 K and 8 T.