A novel large-cell boron nitride polymorph

Abstract

Through density functional theory simulations, the structural properties, stability, mechanical properties, elastic anisotropy as well as electronic properties for boron nitride allotropes with cubic structure, Pn-3n BN, are investigated in this work. Studying the phonon spectra, molecular dynamics as well as elastic constants of Pn-3n BN, it is found that porous Pn-3n BN is stable in dynamics, thermodynamics and mechanics. The B (bulk modulus), G (shear modulus) and E (Young's modulus) of Pn-3n BN are 64 GPa, 26 GPa and 69 GPa, respectively. The B/G (the ratio of bulk modulus to shear modulus) and v (Poisson's ratio) of Pn-3n BN are 2.43 and 0.319, respectively, which exhibit ductility. The three-dimensional surface construction for Young's modulus, the maximum and minimum of shear modulus, the maximum and minimum of Poisson's ratio of Pn-3n BN are all irregular spheres, indicating that Pn-3n BN has elastic anisotropy. The Emax/Emin of Pn-3n BN displays isotropy with 1.00 in (111) plane, and is not equal to 1.00 in other principal planes, showing anisotropy. The conduction band minimum (CBM) and the valence band maximum (VBM) of Pn-3n BN are both located at point G, and the band gap width of Pn-3n BN is 5.197 eV, from which Pn-3n BN is a wide band gap and direct band gap semiconductor material.