Raman spectroscopy of carbon doped MgB₂ prepared using carbon encapsulated boron as precursor

We have studied the surface topographical changes and the Raman spectroscopic modifications for carbon-doped MgB₂ that was fabricated with carbon-encapsulated boron as precursor. Bulk MgB₂ samples of 20 mm diameter and 7 mm thickness were prepared by an in-situ one-step solid state sintering technique. It was found that optimum doping led to the reduction of the average grain size, which was then effective in enhancing flux pinning in MgB₂. For the optimum doped sample, the self-field critical current density J_c at 20 K reached 375 kA/cm². However, T_c values were suppressed with further carbon doping, presumably due to an increase in the disorder in the system, which was demonstrated by a decrease in full width and half maxima of the E_2g mode in the Raman spectra.