Partial nitridation of Li4SiO4 and ionic conductivity of Li4.1SiO3.9N0.1

The Li content and anion lattice of Li₄SiO₄ were modified to improve ionic conductivity. Li₂CO₃ and Si₃N₄ were mixed in a ratio of Li/Si?=?4.5 and heated in NH₃ at 820?°C, which resulted in the formation of the oxynitride, Li_4.1SiO_3.9N_0.1. Powder X-ray diffraction analyses revealed Li_4.1SiO_3.9N_0.1 and Li₄SiO₄ to be isostructural with a subtle variation in the lattice constants. Diffuse-reflectance absorption spectroscopy, however, showed a significant decrease in the band gap, from 5.6?eV in Li₄SiO₄ to 4.8?eV in Li_4.1SiO_3.9N_0.1. X-ray photoelectron spectra of the Li 1s and Si 2p levels revealed enhanced lattice covalency in Li_4.1SiO_3.9N_0.1 compared to the oxide phase. The ionic conductivity of Li₄SiO₄ and Li_4.1SiO_3.9N_0.1 were measured by ac impedance spectroscopy over the temperature range 100–400?°C. Non-linear fitting analysis of the equivalent circuit revealed that the ionic conductivity of Li_4.1SiO_3.9N_0.1 was approximately one order of magnitude higher than that of Li₄SiO₄.