Field-assisted-sintering technique (FAST) has been employed to obtain polycrystalline MgB2 samples, pristine and doped with 5 mol % SiC and B4C, using commercial MgB2 powder. The mass density of the samples is around 90% of the theoretical value. The response in magnetic field shows that the upper critical field and the irreversibility field are depressed by comparison with pristine MgB2. The latter has an upper critical field Hc2=14.37 T close to the values reported for the single crystals. Scaling analysis of the field dependence of the pinning force suggests that both addition of SiC and B4C stabilizes two well defined pinning regimes in FAST-processed MgB2. At low temperatures, T< 24 K (H≤5T), the pinning occurs at the grain boundaries whereas at higher temperatures there is a mixed pinning. These effects are supposed to be the combined result of relatively low level of C diffusion into the lattice of MgB2, specific features in formation of the grain boundaries during FAST processing and the influence of the added materials on morphology. At high fields (above 8.5T) and 4.2K, doped samples are superior to the pristine one from the critical current density viewpoint.
ASJC Scopus subject areas
- Physics and Astronomy(all)