Elastic anisotropy and electronic properties of Si3N4 under pressures

First principles calculations are performed to systematically investigate the electronic structures, elastic, anisotropic and electronic properties of the monoclinic, tetragonal and orthorhombic structures of Si3N4 under pressure. Anisotropy studies show that three Si3N4 phases exhibit a large anisotropy. Furthermore, using the HSE06 hybrid functional, the monoclinic, tetragonal and orthorhombic phases are found to be wide band-gap semiconductors. The pressure induced band gap direct-indirect transition is found for monoclinic Si3N4. The elastic modulus, compressional and shear wave velocities as well as Debye temperatures as a function of pressure in three Si3N4 phases are also investigated in detail.