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Na4Si4and Na4Ge4are ideal chemical precursors for inorganic clathrate structures, clusters, and nanocrystals. The monoclinic Zintl phases, Na4Si4and Na4Ge4, contain isolated homo-tetrahedranide [Si4]4−and [Ge4]4−clusters surrounded by alkali metal cations. In this study, a simple scalable route has been applied to prepare Zintl phases of composition Na4Si4and Na4Ge4using the reaction between NaH and Si or Ge at low temperature (420 °C for Na4Si4and 270 °C for Na4Ge4). The method was also applied to K4Ge4, 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 pure Na4Si4, Na4Ge4or K4Ge4at 420 °C (Na4Si4) or 270 °C (both M4Ge4compounds, M = Na, K). TG/DSC analysis of the reaction of NaH and Ge indicates that ball milling reduces the temperature for reaction and confirms the formation temperature. This method provides large quantities of high quality Na4Si4and Na4Ge4without the need for specialized laboratory equipment, such as Schlenk lines, niobium/tantalum containers, or an arc welder, thereby expanding the accessibility and chemical utility of these phases by making them more convenient to prepare. This new synthetic method may also be extended to lithium-containing Zintl phases (LiH is commercially available) as well as to alkali metal-tetrel Zintl compounds of other compositions, e.g.K4Ge9. [ABSTRACT FROM AUTHOR]

By converting waste heat into electricity and improving the efficiency of refrigeration systems, thermoelectric devices could play a significant role in solving today's energy problems. Increasing the thermoelectric efficiency (as measured by the thermoelectric material's figure-of-merit, zT) is critical to the development of this technology. Complex Zintl phases, in particular, make ideal candidates for thermoelectric materials because the necessary “electron–crystal, phonon–glass” properties can be engineered with an understanding of the Zintl chemistry. A recent example is the discovery that Yb14MnSb11, a transition metal Zintl compound, has twice the zT as the material currently in use at NASA. This perspective outlines a strategy to discover new high zT materials in Zintl phases, and presents results pointing towards the success of this approach. [ABSTRACT FROM AUTHOR]

Capped boron nanoparticles have been synthesized at room temperature by a simple route that does not involve the use of flammable boranes. [ABSTRACT FROM AUTHOR]