Coherent approach to two-dimensional heterolayered oxychalcogenides using molten hydroxides

Heterolayered structures consist of two or more different types of layer and can exhibit exceptional physical properties. Rational routes to synthesize new members of such compounds are required because most of these compounds have been discovered unintentionally. So far there is no generic method to vertically stack chemically different layers to form two-dimensional compounds owing to a lack of understanding of the synthesis of these materials. Here we report the use of molten hydroxides as unconventional solutions for the rapid stacking of oxide and chalcogenide layers with precise composition control. In addition, the crystal growth of heterolayered phases can be achieved by the reaction of different components at their diffusion front in molten hydroxides. This approach creates conditions in which the building blocks for each heterolayer can coexist, enabling heterolayered structures and bypassing the challenges of traditional solid-state chemistry methods where short reactant diffusion lengths predominate. This crystal growth methodology for heterolayers is also applicable to systems that do not form congruent melts at high temperatures. Preparing two-dimensional heterolayers by vertically stacking chemically different layers with multiple anions remains challenging. Now, a general approach for the synthesis of heterolayered oxychalcogenides using molten hydroxides as unconventional solutions for the rapid stacking of oxide and chalcogenide layers with precise composition control is demonstrated.