A straightforward approach to high purity sodium silicide Na4Si4

Abstract

Sodium silicide Na₄Si₄ is a reductive and reactive source of silicon highly relevant to designing non-oxidic silicon materials, including clathrates, various silicon allotropes, and metal silicides. Despite the importance of this compound, its production in high amounts and high purity is still a bottleneck with reported methods. In this work, we demonstrate that readily available silicon nanoparticles react with sodium hydride with a stoichiometry close to the theoretical one and at a temperature of 395 °C for shorter duration than previously reported. This enhanced reactivity of silicon nanoparticles makes the procedure robust and less dependent on experimental parameters, such as gas flow. As a result, we deliver a procedure to achieve Na₄Si₄ with purity of ca. 98 mol% at the gram scale. We show that this compound is an efficient precursor to deliver selectively type I and type II sodium silicon clathrates depending on the conditions of thermal decomposition.