Effects of Hydrostatic Pressure and Biaxial Strains on the Elastic, Electronic and Lattice Vibrational Properties of Trigonal Boron Nitride

The effects of hydrostatic pressure and biaxial strains on the elastic, electronic, and lattice vibrational properties of a new superhard material trigonal boron nitride ( T ‐BN) are studied by first‐principles calculation. The mechanical and dynamical stabilities of T ‐BN are confirmed by elastic constants criteria and phonon dispersion curves. It is found that all elastic constants and elastic modulus increase (decrease) under pressure and compressive (tensile) strainϵ x x. The Vicker's hardness of every single chemical bond as well as the crystal is calculated by a microscopic model. The hardness of T ‐BN 55.5 GPa is smaller than that in c ‐BN (64 GPa) but increases significantly with increasing pressure and compressiveϵ x x. The anisotropic index and anisotropic velocities, as well as the Debye temperature for T ‐BN are also discussed. Moreover, the computational infrared absorption spectra exhibit significant blueshift under pressure and − 5 % < ϵ x x < 3 % , while redshift of A 3 and E 4 modes can be observed whenϵ x x > 3 % . Electronic calculation shows the T ‐BN is an indirect band‐gap semiconductor, and energy gap decreases monotonically under computational conditions. Analysis based on density of states is conducted, clarifying the causes of bonding and bandgap changes in T ‐BN.