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,2 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 mu H-o(c2) from 20.5 T for pure sample to more than 33 T and enhancement of mu H-o(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 mu H-o(irr) and mu H-o(c2) respectively we obtained with only 2 K drop in the T-c.