Microwave initiated solid-state metathesis routes to Li2SiN2

Abstract

The fast ion conductor lithium silicon nitride, Li₂SiN₂, is produced in a metathesis reaction between silicon chloride, SiCl₄, and lithium nitride, Li₃N, initiated in a conventional microwave oven. Lithium amide, LiNH₂, and ammonium chloride, NH₄Cl, serve to control the temperature and enhance the yield of Li₂SiN₂. A reaction mechanism is proposed based on the exothermicity of forming the by-product salt lithium chloride with silicon nitride, Si₃N₄, as a likely intermediate. By varying the stoichiometry of the reactants the phase LiSi₂N₃ can also be produced. The Li₂SiN₂ product is characterized using powder X-ray diffraction, scanning electron microscopy and complex impedance spectroscopy. A pressed pellet of Li₂SiN₂ has a conductivity of 2.70 × 10⁻³ S cm⁻¹ at 500 °C.