First-principles investigation of the structural, electronic and optical properties ofolivine-Si3N4 and olivine-Ge3N4

Abstract

Si3N4 and Ge3N4 are important structural ceramics with many applications because of their outstandinghigh-temperature and oxidation-resistant properties. Two stable phases of them,α and β, have thus far been synthesized. The high-pressure and high-temperature spinelphases of these two materials were noticed to have wide, direct electronic bandgaps that are comparable to those of the promising newly developed solid-stateoptoelectronic materials such as lasers and LEDs. Another high-pressure andhigh-temperature phase, the olivine phase, has also attracted attention recently. In thepresent work, the structural and electronic properties of the new olivine nitridesSi3N4 and Ge3N4 are studied by the FLAPW method with PBE-GGA exchange and correlation potential. Thestability of the two materials and the transition pressure are investigated. It is found thatolivine-Ge3N4 is not stable and is difficult to be observed, whileolivine-Si3N4 can be synthesized under appropriate conditions. The atomic sites have been optimized andthe ground-state properties such as equilibrium lattice constant, bulk modulus, bandstructure and density of states have been obtained. Furthermore, the dielectric function hasbeen calculated based on the random phase approximation.