Control of nano carbon substitution for enhancing the critical current density inMgB2

Abstract

The effects on transition critical temperature, lattice parameters, critical current density, and flux pinningof doping MgB2 with carbon nanoparticles, were studied for bulk, wire and tape under a widerange of processing conditions. Under the optimum conditions, magneticJc was enhanced by two orders of magnitude at 5 K for a field of 8 T, and by a factor of 33 at 20 K for afield of 5 T for bulk samples, whereas enhancement by a factor of 5.7 was observed in the transportIc at 12 T and 4.2 K for a wire sample. Samples sintered at high temperature (900 and1000 °C) exhibitedexcellent Jc,approximately 10 000 A cm−2 in fields up to 8 T at 5 K. This result indicates that flux pinning was enhanced by thecarbon substitution for B with increasing sintering temperature. Highly dispersednanoparticles are believed to enhance the flux pinning directly, in addition to theintroduction of pinning centres by carbon substitution. Nano-C is proposed to be one of themost promising dopants besides SiC and CNT for the enhancement of flux pinning forMgB2 in high fields.