High critical field NbC superconductor on carbon spheres

Abstract

Niobium carbide (NbC) nanoparticles embedded on the surface of carbon spheres (CS) were synthesized at 1350 °C by the carbothermal reduction of niobium oxide precursor in flowing argon (Nbc@CS). The morphology, crystal structure, and magnetic properties of the hybrid nanocomposite were investigated by means of electron microscopy, X-ray diffraction and a superconducting quantum interference device. It was found that the NbC@CS nanocomposites exhibit type-II superconductivity with a critical temperature (T_c) of 8–12 K, typical for stoichiometric NbC. The superconducting hysteresis loop reveals several interesting traits, including strong vortex pinning, the presence of asymmetry and a high penetration field. Moreover, the sample shows much improved irreversible (H_irr), lower (H_c1) and upper (H_c2) critical fields. The coherence length (ξ), penetration depth (λ), and Ginzburg–Landau (κ) parameters for the sample were estimated to be 9.78 nm, 33 nm and 3.39, respectively.