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 Jc at 20 K reached 375 kA/cm2. However, Tc 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 E2g mode in the Raman spectra.
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