Effects of biaxial strains on the structural, electronic, elastic and lattice vibrational properties in t-BC2N and z-BC2N

Abstract

The effects of in-plane biaxial strains on the structural, electronic, elastic and lattice dynamical properties of tetragonal t-BC2N and z-BC2N are investigated using first-principles calculations within generalized-gradient approximation (GGA) and HSE06 range-separated hybrid functionals. We find that all the elastic constants, bulk, shear and Young’s moduli decrease (increase) almost linearly with increasing tensile (compressive) strains. However, strain-induced changes in band gaps are highly asymmetric and nonlinear. t-BC2N undergoes an indirect → direct band-gap transition at εxx = −1.36%, whereas z-BC2N is always a direct band-gap material for −2.5% < εxx < 2.5%. The crystal-field splitting energy Δcf decreases from positive to negative at a certain tensile strain. The infrared(IR)-active phonon frequencies exhibit substantial red (blue) shifts under tensile (compressive) strains. The atomic displacement patterns corresponding to typical strong IR-active vibrational modes are analysized. Our calculated results show that strain can serve as an exploitable tool for engineering physical properties of t-BC2N and z-BC2N.