Mechanism of the formation of structure during high-temperature annealing of MgB$_{2}$ bulk samples deformed under pressure

MgB$_{2}$ superconductors subjected to deformation under pressure on Bridgeman anvils and subsequent annealings at 800 and 950$^\circ$C were investigated by X-ray diffraction, scanning electron microscopy, and microanalysis. It was shown that at these temperatures crystals of MgB$_{2}$ phase along the residual boron dissolute in the residual liquid magnesium with the formation of both dense and loose areas of MgB$_{2}$ phase. The latter has a negative influence on critical current. At the same time, after these treatments, the samples become more uniform by the phase and chemical composition.