  The influence of the oxygen segregation into Mg-B-O inclusions (which are
oxygen enriched as compared to the matrix material) and the formation of boron
enriched phases (with near MgB12 composition) in MgB2 structure on pinning in
magnesium diboride and the effect of SiC and Ti alloying on the formation of
structural inhomogenities in MgB2 are discussed. A nanostructural material of
near theoretical density (2.7 g/cm3) based on MgB2-SiC (10 wt. percents of
200-800 nm SiC was added), which is characterized by high jc (1000000 A/cm2 in
1 T - 100000 A/cm2 in 3.5 T at 20 K and 100000 A/cm2 at 35 K) has been
synthesized at 2 GPa.
