Impact of Carbon-Based Doping on the Structural and Superconducting Properties of MgB2: A Comparative Study

Investigation of the influence of various carbon-based dopants, specifically carbon nanotubes (CNT), glutaric acid, melanin, boron carbide (B₄C), silicon carbide (SiC), and glucose, on the structural and superconducting properties of magnesium diboride (MgB₂) has been studied. The analysis conducted via X-ray diffraction (XRD) revealed modifications in peak positions, which can be attributed to lattice strain, with samples incorporated with melanin demonstrating the most pronounced alterations. This lattice strain led to a reduction in electron density within the σ hole band, consequently exerting a detrimental effect on superconductivity. Resistivity measurements indicate a reduction in the critical temperature (T_c) for all doped samples, with values ranging from 38.1 K (for pure) to 36.8 K (for melanin). Upon the assessment of critical current density (J_c), samples doped with SiC, CNT, glucose, and B₄C revealed significant enhancements at a magnetic field of 3 T (operating field of MRI). The highest J_c values were achieved at 7.2 × 10⁴ A/cm² at 5 K (CNT and GL) and 1.66 × 10⁴ A/cm² at 20 K for CNT. Collectively, the dopants CNT and SiC provided an optimal balance of lattice strain, grain connectivity, and flux pinning, leading to enhanced superconducting attributes across the comprehensive range of magnetic fields.