Effect of various additions on upper critical field and irreversibility field of in-situ MgB2 superconducting bulk material

The effect of silicon carbide, carbon and metal-diboride (NbB₂, ZrB₂, and TiB₂) additions on the irreversibility field, H_irr and the upper critical field H_c2 of bulk superconducting MgB₂ have been studied. Samples with 10 mole % of SiC and C and 7.5% of above named metal diboride additions were made separately by a powder milling and compaction technique along with the control sample. These samples were heat-treated at various schedules and H_c2 and H_irr values were measured. An increase in μ_oH_c2 from 20.5 T for pure sample to more than 33 T and enhancement of μ_oH_irr from 16 T to a maximum of 28 T for SiC doped sample was observed at 4.2 K. For a ZrB₂ doped sample 24 T and 28.6 T of μ_oH_irr and μ_oH_c2 respectively we obtained with only 2 K drop in the T_c.