Unique Roles of PVP-Derived Carbon Dopant in Tailoring Microstructure and Elevating High-Field Jc and Hc2 for Pressure-Assisted Infiltration-Processed MgB2 Bulks

Abstract

Abstract

Abstract The rapid decay of the critical current density (Jc) of MgB2 in high magnetic fields remains a major barrier to its practical use. Although carbon doping is an established strategy to strengthen flux pinning and enhance the upper critical field (Hc2), conventional carbon dopants are prone to agglomeration, which can deteriorate intergrain connectivity and reduce the effective cross-sectional area available for current transport. Herein, polyvinylpyrrolidone (PVP) is verified as a superior organic carbon precursor, and pressure-assisted Mg infiltration is adopted to fabricate PVPdoped MgB2 bulks. Benefiting from PVP pyrolysis, in-situ introduced carbon triggers evident lattice contraction and remarkable grain refinement alongside heterogeneous carbon-enriched domains inside the matrix: partial PVP-derived carbon atoms substitute boron lattice sites, whereas residual carbon-rich precipitates refine crystalline grains and serve as abundant extrinsic flux-pinning centers. More importantly, PVP decomposition intermediates effectively suppress the generation of MgO impurity during sintering and lower the MgO phase proportion, an exclusive merit unavailable for many inorganic carbon dopants. Owing to above merits, high-field superconducting properties are markedly improved, and the 10 wt% PVP-doped sample presents the best performance. At 20 K and 5 T, its critical current density reaches 1.46×103 A/cm2 , approximately 8.5 times that of the undoped counterpart; at 5 K under 7 T, the value rises to 2.01×104 A/cm 2 , nearly an order of magnitude superior to the pristine sample. Meanwhile, this optimal specimen delivers an irreversibility field of 9.58 T and an upper critical field of 12.05 T at 20 K. These results demonstrate that PVP serves as a high-efficiency and versatile organic carbon precursor for prominently boosting the high-field superconducting performances of MgB2 bulks. This facile and feasible PVP doping strategy can effectively integrate impurity suppression, flux pinning reinforcement and well-preserved grain connectivity, overcoming the performance bottlenecks of conventional carbon modification methods.