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

Abstract

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) strain ϵxx. 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 compressive ϵxx. 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%<ϵxx<3%, while redshift of A3 and E4 modes can be observed when ϵxx>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.

Prediction of Superhard BN2 with High Energy Density*

“…Boron and nitride can easily form strong covalent bonds at high pressure, and much research effort has explored superhard boron nitride materials such as 𝑐-BN, [3,4] 𝑤-BN, [33] 𝑝-BN, [34] 𝑏𝑐𝑡-BN, [35] 𝑜-BN, [35,36] M-BN, [37] 𝑃 𝑚𝑛2 1 BN, [38] 𝑡-BN, [39] 𝑐𝑚-BN, [40] Z-BN, [41] 𝑃 𝑏𝑐𝑎-BN, [42] and 𝑝𝑐𝑡-BN, [43] which possess estimated Vickers hardness values of 47-67 GPa. Recently reported non-stoichiometric B-N compounds, such as B 6 N, [44,45] B 3 N 5 , [46] B 3 N 4 , [47] B 2 N 3 , [48] B 13 N 2 , [49−53] are potential new superhard materials.…”