Abstract

Carbon was known to be one of effective additives which can improve the flux pinning of MgB_2 at high magnetic fields. In this study, glycerin (C_3H_8O_3) was selected as a chemical carbon source for the improvement of critical current density of MgB_2. In order to replace some of boron atoms by carbon atoms, the boron powder was heat-treated with liquid glycerin. The glycerin-treated boron powder was mixed with an appropriate amount of magnesium powder to MgB_2 composition and the powder pallets were heat treated at 650°C;and;900°C for 30 min in a flowing argon gas. It was found that the superconducting transition temperature (T_c) of Mg(B_1-xC_x)_2 prepared using glycerin-treated boron powder was 36.6 K, which is slightly smaller than T_c(37.1 K) of undoped MgB_2. The critical current density (J_c) of Mg(B_1-xC_x)_2 was higher than that of undoped MgB_2 and the T_c improvement effect was more remarkable at higher magnetic fields. The T_c, decrease and J_c increase associated with the glycerin treatment for boron powder was explained in terms of the carbon substitution to boron site.

• Keywords: MgB_2 superconductor;Glycerin treatment;Carbon doping;Critical current density;