In situ identification of kinetic factors that expedite inorganic crystal formation and discovery

Navigating the kinetic landscape is a key to reaching complex inorganic phases efficiently. High-temperature treatment of elemental mixtures is the traditional method of solid-state syntheses, where thermodynamic driving forces are large, but success can be hampered by kinetic barriers. Successful inorganic crystal preparation relies on methods to either surmount such barriers, or direct the reaction to avoid them. Both approaches were utilized in our synthetic investigation with in situ X-ray diffraction (XRD) using Fe₂SiS₄ as the target compound. In this system, Si sulfidation is the limiting factor preventing thermodynamic Fe₂SiS₄ crystal formation. Through in situ XRD reaction maps, we established that superheated S liquid from the FeS₂ peritectic at 743 °C was responsible for the onset of rapid Fe₂SiS₄ formation. Alternatively, by pre-reacting Si with Fe, we directed the chemical system via intermediate states that expedited Fe₂SiS₄ formation at temperatures as low as 550 °C. The utilization of these kinetic expediting factors, and those that can be uncovered by similar methods, can improve the potential of the solid state method for creating new materials and refining chemical syntheses.