Rapid solid-state synthesis of materials from molybdenum disulphide to refractories

Abstract

LAYERED molybdenum and tungsten dichalcogenides have stimulated considerable interest as lubricants^1,2, battery cathodes^3–5, and catalysts^6–8. Pure, crystalline group VI transition-metal dichalcogenides are normally prepared by intermittently grinding and heating the elements at >900 °C for several days. Low-temperature solution routes to these materials have also been explored^9–11. In those studies, exchange (metathesis) reactions between transition-metal halides and alkali-metal sulphides or covalent sulphiding agents in polar organic solvents were found generally to yield finely divided products at close to ambient conditions. Here, in contrast, we consider the factors that influence reactions between transition-metal halides and alkali-metal chalcogenides in the solid state. These highly energetic reactions, driven by the formation of very stable product species, provide a powerful method for the rapid synthesis of materials normally prepared at high temperatures over long periods of time. Other advantages of these solid-state reactions include control of reaction conditions and of product particle sizes. Although our study focuses on group VI transition-metal dichalcogenides, analogous metathesis reactions can be used for rapid syntheses, initiated at low temperatures, of many other technologically important materials.