Fabrication and Characterisation of Nano-doped and Pure Magnesium Diboride Superconductors

Abstract

The effect of SiC by diffusion method shows the broadening of full width at half maximum values in x-ray diffraction patterns with the increasing of the doping level; indicates smaller grains and imperfect MgB2 crystallinity. Jc enhancement by different doping level at respective temperature suggests, impurities such as Mg2Si, MgB2C2 and MgO play a significant role in 20 K while carbon substitution effect dominances the flux pinning in 5 K. This investigation demonstrates that flux pinning and the Jc can be tailored for various applications depending on the operating temperature and external magnetic field. We have investigated the effects of nano-carbon doping at low doping (2.5%) and high doping (10%) as the intrinsic (B-site nano-carbon substitution) and extrinsic (nano-carbon derivatives) pinning by diffusion method. This work shows that the Jc ~104 A/cm2 value prepared by the in situ method doped with 5% nano-carbon at 4 T and 20 K is achievable with a lower doping level, 2.5% nano-carbon doped prepared by this method. At high doping, the presence of B4C region blocked the Mg from reacting with crystalline B thus hampering the formation of MgB2. Furthermore, the unreacted Mg acted as a current blocking phase in lowering the grain connectivity hence depressing the Jc of the 10% nano-carbon doped MgB2 bulk superconductor. Finally, a new approach in extracting the important information on the microstructure and the texture of MgB2 superconductors in a precise manner is presented for the first time here by using the transmission Kikuchi diffraction in the scanning electron microscope technique. The new technique offers a better spatial resolution compared to conventional electron backscattered diffraction. This information is useful to understand the superconducting properties and to guide the fabrication and processing of the MgB2 superconductor in the future.