In materials synthesized from Mg and B taken in the magnesium diboride stoichiometry under high-pressure 2 GPa in 973 K -1373 K temperature range the inhomogeneities  of size about 200 microns and below like as grains of magnesium dodecaborides and grains with higher oxygen concentration can be observed  The larger amount and finer distribution of dodecaboride grains correlate with higher pinning force and higher critical current density. On the one hand, an increase of the synthesis temperature leads to a decrease of the amount of magnesium dodecaboride in the structure and on the other provokes the segregation of oxygen-enriched phase into the fine homogeneously dispersed grains, which can promote pining as well. This can explain the fact that as the synthesis temperature increases from 1073 K to 1323 K, two local maximums of critical currents at the beginning and the end of this temperature range can be observed. 

The extremely high critical current densities were attained for the material with SiC added to the stoichiometric MgB₂ mixture of magnesium and amorphous boron with 0.66 % of oxygen when synthesized at 2 GPa,  1050 ^oС for 1 h: in zero magnetic field it reached 1.6×10⁶A/cm² at 10 K and 1.24×10⁶A/cm² at 20 K,  was above 10⁶ A/cm² in the fields up to  2 and 1 T at 10 and 20 K, respectively, and higher than 10⁵ A/cm² in the fields up to 5 and 3.5 T at 10 and 20 K, respectively. The field of irreversibility at 20 KJ was higher than 8 Tand at 10 T in 10 T field the critical current density exceeded 1000 A/cm². By adding SiC in the amount of 10 wt % in the case of synthesis at 1050 ^oC (under 2 GPa) the critical current density of the material can be increased by a factor of 1.4-10 (in magnetic fields from 0 to 10 T  at 10 K and in magnetic fields from 0 to 6 T at 20 K).

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