Significant enhancement of critical current density and flux pinning in MgB 2 with nano-SiC, Si, and C doping

Abstract

Polycrystalline MgB 2 samples with addition of 0–10 wt% powders of SiC, Si and C were prepared by an in situ reaction process. The phases, microstructures, and flux pinning were characterized by XRD, TEM, and magnetic measurements. It was observed that the samples doped with nano-sized SiC have best pinning performance, while nano-Si or nano-C powders showed a similar improved field dependence of the critical current over a wide temperature range compared with both undoped samples and samples doped with coarse SiC and Si powders. Both magnetic and transport J c were as high as 3000–20,000 A/cm 2 in 8 T at 5 K, one or two orders of magnitude higher than for undoped MgB 2. T c only dropped 2 K and remained unchanged with high doping levels for these doped samples. X-ray diffraction results indicated that Si and SiC had reacted with Mg to form Mg 2Si. Neutron diffraction and Rietveld analysis showed no evidence of Si doping into the lattice in the Si doped MgB 2 samples. Nano-particle inclusions, such as Mg 2Si, precipitates of MgO, unreacted nano-particles observed using TEM are proposed to be responsible for the enhancement of flux pinning in high fields. A strong effect of sample size on magnetic J c( H) was also observed for bulk MgB 2.