Substantial increment in critical parameters of MgB2 superconductor by boron site nano-carbon substitution

This paper deals with the determination of critical properties of MgB2 along with the impact of carbon substitution on critical parameters. The change in lattice parameters and decrease of transition temperature, T-c confirms the successful substitution by carbon at boron site. The magneto transport measurements up to 140 kOe are carried out to determine upper critical field (H-c2). The upper critical field values, H-c2 are obtained from rho-T(H) data based upon the criterion of 90% of normal resistivity. The Ginzburg Landau theory (GL equation) is applied to the rho-T(H) data which accounts for the temperature dependence behavior of H-c2 in the low temperature high field region along with the determination of H-c(0) value. The H-c(0) value of about 300 kOe is obtained for the carbon doped sample while the same is just near to 160 kOe for the pure MgB2 sample. (C) 2009 Elsevier B.V. All rights reserved.