Solutions of lithium salts in liquid lithium: interaction between silicon and nitrogen to form the ternary compound, Li5SiN3

Abstract

The interaction between silicon and nitrogen when dissolved in liquid lithium (mol fraction Li 0.97) at 750 K has been monitored using electrical resistivity methods. Resistivity–time data indicate that an insoluble product is formed and that the kinetics of the various dissolution and precipitation processes are such that addition of gaseous nitrogen to Li–Li₂₂Si₅ solutions leads to a homogeneous solution reaction, whereas addition of solid silicon to Li–Li₃N solutions leads to a heterogeneous reaction mechanism at the solid–liquid interface. Resistivity–concentration data show that the reaction product has a Si : N ratio of approximately 1 : 3. X-ray powder diffraction studies of the product when embedded in the lithium matrix and when isolated from the lithium (by vacuum distillation of excess lithium) confirm its identity as Li₅SiN₃. This material was also obtained from the corresponding 875 K solid state reaction between 1 : 3 and 1 : 4 mol ratios of Li₂₂Si₅ and Li₃N. Both Li₂SiN₂ and Li₈SiN₄ were also prepared, characterised by X-ray powder diffraction methods, and their stabilities to vacuum distillation conditions ascertained.