Defects in boron carbide: First-principles calculations and CALPHAD modeling

The energetics of defects in B4+xC boron carbide and β-boron are studied through first-principles calculations, the supercell phonon approach and the Debye–Grüneisen model. It is found that suitable sublattice models for β-boron and B4+xC are B101(B,C)4 and B11(B,C) (B,C,Va) (B,Va) (B,C,Va), respectively. The thermodynamic properties of B4+xC, β-boron, liquid and graphite are modeled using the CALPHAD approach based on the thermochemical data from first-principles calculations and experimental phase equilibrium data in the literature. The concentrations of various defects are then predicted as a function of carbon composition and temperature.