Domains of the phases V$_8$C$_7$ and V$_3$C$_2$ in bulk carbide VC$_y$

The formation of cubic (V$_8$C$_7$) and orthorhombic (V$_3$C$_2$) superstructures at the upper and lower boundaries of the homogeneity interval of nonstoichiometric vanadium carbide VC$_y$ has been studied. It has been found that the composition of the ordered phase V$_8$C$_{7-\delta}$ deviates from the composition of the ideal superstructure V$_8$C$_7$ because of the reduced filling factor of 4(a) site of the nonmetal sublattice of carbon atoms. Vanadium atoms forming the octahedral environment $\square$V$_6$ of vacant sites in the phases V$_8$C$_7$ and V$_3$C$_2$ are displaced toward a vacancy. Early stages of the formation of domains of ordered phases have been studied. The effect of the quenching and annealing temperatures on the dimension of domains has been determined. In bulk vanadium carbide, the formation of domains of ordered phases begins at the grain boundaries of disordered carbide VC$_y$ and results in the appearance of a domain nanostructure.