Effects of Hydrostatic Pressure and Biaxial Strains on the Elastic and Electronic Properties of β‐Si3N4

Abstract

First principles calculations have been performed to investigate the effects of hydrostatic pressure and biaxial strains (ϵxx) on the electronic and elastic properties of β‐Si3N4. Both bulk modulus and Vickers hardness enhance (decrease) with pressure and compressive (tensile) ϵxx. The evolution of BH/GH ratio indicates that β‐Si3N4 has a better (worse) ductile behavior under pressure and compressive (tensile) ϵxx. The 3D plots of Young's modulus show huge difference in mechanical properties between [0001] direction and a‐b plane and the anisotropy becomes larger by using strain engineering. The sound velocities and Debye temperature are also discussed. The energy gap increases monotonically with pressure, however, strain‐induced changes in band gap are asymmetric and nonlinear. β‐Si3N4 undergoes an indirect to direct band gap transition at biaxial strain of 5%, while β‐Si3N4 is always an indirect band gap semiconductor under pressure and compressive strains.