First-principles investigation on the mechanical, dynamical and thermodynamic properties of some B12-based compounds under hydrostatic pressure

Abstract

The mechanical, dynamical, and thermodynamic properties of some B₁₂-based compounds with a rhombohedral structure were studied by the first-principles method from P = 0–350 GPa. The elastic moduli, Poisson's ratio, crystal anisotropy, Vickers hardness, fracture toughness, and Debye temperature of all compounds were calculated using elastic constants. We found that the calculated Debye temperatures were above 1075 K for all compounds, indicating that the examined materials were quite hard. Although all compounds exhibited a brittle structure depending on the B_H/G_H ratio at ambient pressure, they exhibited ductile structures with increasing pressure. Although all compounds exhibited a brittle structure depending on the B_H/G_H ratio at ambient pressure. Soft modes were not observed in the phonon distribution curves calculated at ambient pressure, and all compounds were dynamically stable. The entropy, heat capacity, free energy, and internal energy functions representing the thermodynamic properties of the compounds depending on the temperature were computed. Predictions are made for many physical quantities of some B₁₂-based compounds for which no experimental data are available.