Effect of nano-carbon particle doping on the flux pinning properties of MgB2 superconductor

TL;DR

This study investigates how nano-carbon doping affects flux pinning and superconducting properties of MgB2, showing improved high-field current density with minimal Tc reduction due to nano-inclusions and substitution effects.

Contribution

It provides detailed analysis of nano-carbon doping effects on MgB2's microstructure and flux pinning, highlighting the role of nano-inclusions and substitution in enhancing performance.

Findings

Nano-C doping improves Jc in high magnetic fields.

Tc decreases slightly with increased doping levels.

Nano-inclusions of Mg2C3 and MgB2C2 are responsible for flux pinning enhancement.

Abstract

Polycrystalline MgB2-xCx samples with x=0.05, 0.1, 0.2, 0.3, 0.4 nano-particle carbon powder were prepared using an in-situ reaction method under well controlled conditions to limit the extent of C substitution. The phases, lattice parameters, microstructures, superconductivity and flux pinning were characterized by XRD, TEM, and magnetic measurements. It was found that both the a-axis lattice parameter and the Tc decreased monotonically with increasing doping level. For the sample doped with the highest nominal composition of x=0.4 the Tc dropped only 2.7K. The nano-C-doped samples showed an improved field dependence of the Jc compared with the undoped sample over a wide temperature range. The enhancement by C-doping is similar to that of Si-doping but not as strong as for nano-SiC doped MgB2. X-ray diffraction results indicate that C reacted with Mg to form nano-size Mg2C3 and MgB2C2 particles. Nano-particle inclusions and substitution, both observed by transmission electron microscopy, are proposed to be responsible for the enhancement of flux pinning in high fields.