Electronic, optical and mechanical properties of SrSi6N8 and SrSi6N8O via first-principles

Abstract

The different properties of two structurally similar nitridosilicates, SrSi₆N₈ and SrSi₆N₈O, are attributed to the oxygen atom. To explore the effects of the O atom on the properties, structural, electronic, optical and mechanical properties of SrSi₆N₈, SrSi₆N₈O and O-doped SrSi₆N₈ have been simulated via first-principles in this work. The results indicate the Si–O–Si bond is stronger than the Si–Si bond, resulting in a more stable crystal structure of SrSi₆N₈O compared with SrSi₆N₈. The calculated bandgaps (E_g) of SrSi₆N₈ and SrSi₆N₈O are 3.10 and 3.97 eV, respectively. The lower E_g of SrSi₆N₈ originates from the Si–Si σ* bond, however, the E_g can be enlarged through introducing the O atom into the Si–Si bond. The optical properties illustrate that the refractive peaks are blue-shifted with O doping into the lattice of SrSi₆N₈. Furthermore, the elastic properties show that SrSi₆N₈ and SrSi₆N₈O are comparable to traditional mechanical ceramics such as sialons. This work not only expounds the difference between SrSi₆N₈ and SrSi₆N₈O, but also gives theoretical foundation for their potential applications as optical and mechanical materials.