Microscopic unravelling of nano-carbon doping in MgB2 superconductors fabricated by diffusion method
We investigated the effects of nano-carbon doping as the intrinsic (B-site nano-carbon substitution) and extrinsic (nano-carbon derivatives) pinning by diffusion method. The contraction of the in-plane lattice confirmed the presence of disorder in boron sublattice caused by carbon substitution. The increasing value in full width half maximum (FWHM) in the X-ray diffraction (XRD) patterns with each increment in the doping level reveal smaller grains and imperfect MgB2 crystalline. The strain increased across the doping level due to the carbon substitution in the MgB2 matrix. The broadening of the Tc curves from low to high doping showed suppression of the connectivity of the bulk samples with progressive dirtying. 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 down the grain connectivity hence depressing the Jc of the 10% nano-carbon doped MgB2 bulk superconductor.
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