Inorganic materials are prized for their stability, robust electronic transport, and the huge variety of functional properties that can be engineered by substitutions across the periodic table. Finding new inorganic materials is a crucial step to increase energy efficiency and enable new technologies. But traditional inorganic materials discovery is typically a slow process where reactions are examined ex situ—after a high-temperature reaction has finished and cooled down.
We investigated a class of reactions called liquid flux reactions, where an inorganic salt, in this case K2S3 and K2S5, are melted between 200-300°C and serve as a liquid bath for the reaction. The effect is that the reactions can occur at low temperatures, on fast time scales, and produce different products than traditional high-temperature methods. By conducting these reactions in situ at the Advanced Photon Source, watched the reactions progress in real time and gained a first glimpse of the transient products that precipitate and dissolve in and out of the liquid.
By watching eight different reactions of Cu and Sn in potassium sulfide fluxes, we identified four new phases in only 16 hours of total experiment time. One of these materials, K5Sn2S8, is a new structure type, meaning the atoms are arranged in a repeating pattern that is unlike any known material. We are able to identify many new phases quickly because their formation does not obey the conventional model of crystal growth. They form upon heating the reaction mixture, rather than cooling, so traditional ex situ experiments would never find these phases—they would disappear into the melt after being cooled from high temperature. Our method of in situ synthesis allows us to identify and them isolate them quickly.
In addition to demonstrated a new path toward fast materials discovery, this work is an important step toward being able to control the driving forces behind materials assembly, and thereby can enable the grand challenge of inorganic materials synthesis by design.
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