Research of electronic structures and optical properties of Na- and Mg-doped β-Si3N4 based on the first-principles calculations

The atom population, electronic structures, and optical properties of Na- and Mg-doped β-Si3N4 are investigated by first-principles calculations with the generalized gradient approximation (GGA). Calculated binding and formation energies are −203.4665, −206.4901 eV and 12.8144, 9.7907 eV, respectively, suggesting that the stability increases gradually. The dropped bond population illustrates a decline in bond strength of covalent bond occurs. As obtained electron density difference pictures show that the electron missing near the Si atom between Si and N atoms turns into electron enrichment in terms of Mg intervention compared to undoped field, weakening the strength of the covalent bond. The static dielectric constant obtained at the zero frequency of the real part increases notably to 20.23 after Na doping, and markedly comes to 32.85 for Mg doping, implying its potential applications in electrics and optics. The absorption band ranges of doped systems become narrower. Both of reflectivity spectra profiles are similar and all locate at 12.5 and 15 eV, exhibiting the characteristics of some isotropy. In theoretical electron energy loss spectra, the host peaks of doped systems all locate at about 15 eV, signifying that a red-shift phenomenon occurs after doping.