A versatile low temperature synthetic route to Zintl phase precursors: Na4Si4, Na4Ge4 and K4Ge4 as examples

Abstract

Na 4 Si 4 and Na 4 Ge 4 are ideal chemical precursors for inorganic clathrate structures, clusters, and nanocrystals. The monoclinic Zintl phases, Na 4 Si 4 and Na 4 Ge 4 , contain isolated homotetrahedranide [Si 4 ] 4− and [Ge 4 ] 4− clusters surrounded by alkali metal cations. In this study, a simple scalable route has been applied to prepare Zintl phases of composition Na 4 Si 4 and Na 4 Ge 4 using the reaction between NaH and Si or Ge at low temperature (420 °C for Na 4 Si 4 and 270 °C for Na 4 Ge 4 ). The method was also applied to K 4 Ge 4 , using KH and Ge as raw materials, to show the versatility of this approach. The influence of specific reaction conditions on the purity of these Zintl phases has been studied by controlling five factors: the method of reagent mixing (manual or ball milled), the stoichiometry between raw materials, the reaction temperature, the heating time and the gas flow rate. Moderate ball-milling and excess NaH or KH facilitate the formation of

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