Superconducting Properties of SiC Doped MgB2 Formed Below and Above Mg\´s Melting Point

The fundamental reaction of Mg + B to MgB₂ formation was investigated in order to improve the connectivity of the reacted strands, dopant diffusion, and ultimately the transport properties. Initially, differential scanning calorimetry (DSC), studies were performed to determine the thermodynamics of the solid-state reaction. It was consistently evident from the DSC scans that the formation of the MgB₂ phase was completed below the Mg melting point (~ 655degC). Efforts were made to characterize and understand the differences between the microstructures resulting from the high temperature (above 655degC) and the low temperature (below 655degC) heat-treatments. Transport properties (4.2 K, mostly) of the MgB₂ strands, synthesized by the in-situ reaction between mixed Mg and B powders with 5% or 10% of SiC, both above and below the Mg melting point were measured. The results were correlated with the reaction temperatures. Transport J_cs of the order of 4.8 times 10⁴ A/cm² at 8 T and a B_c2 of 22 T (both at 4.2 K) were obtained for the lower temperature HTed samples, these J_cs are higher than those measured on samples reacted above the Mg melting temperature.