Structural, mechanical, electronic, and thermodynamic properties of dense B 3 N 4 under high pressure predicted from first principles

Five dense B 3 N 4 structures are established by substitution of C atoms with B atoms in the five hypothetical dense C 3 N 4 phases. The structural, elastic, and electronic properties of the five B 3 N 4 polymorphs are investigated through the first‐principles calculations. Our calculations indicate that c ‐B 3 N 4 is energetically favorable in the five structures. Through the calculations of formation enthalpy, we conclude that the B 3 N 4 polymorphs are thermodynamically stable at zero pressure except for the c s ‐B 3 N 4 . The elastic moduli of the five B 3 N 4 polymorphs are calculated using the Voigt–Reuss–Hill approximation. The calculated bulk modulus of c s ‐B 3 N 4 (337 GPa) is the highest of them. The c ‐B 3 N 4 , with shear modulus of 248 GPa, might be a potentially ultra incompressible and hard material. By the elastic stability criteria, it is predicted that the c s ‐B 3 N 4 , c ‐B 3 N 4 , and p ‐B 3 N 4 are mechanically stable within 100 GPa, while the β ‐B 3 N 4 and α ‐B 3 N 4 become mechanically unstable when pressure increases to 30 and 80 GPa, respectively. The calculated B/G ratios indicate that c s ‐B 3 N 4 and p ‐B 3 N 4 possess a ductile nature within 100 GPa. The c ‐B 3 N 4 possess a brittle nature at 0 GPa, as it begins to be prone to ductility, when the pressure increases to 90 GPa. The calculated band structures and densities of states show that all the five B 3 N 4 phases are insulative. Through the quasiharmonic Debye model, we also investigated the thermodynamic properties of these B 3 N 4 polymorphs.