High-entropy materials (HEMs) are an emerging field that has expanded well beyond their origins in metal alloys and now include the materials that are fundamental to ceramics (i.e. oxides, carbides, and nitrides).  The driving concept for high-entropy materials is similar across all material classes, where the equimolar concentration of elements, the incorporation of multiple elements, and the homogeneous distribution of elements in the structure maximize configurational entropy. High-entropy oxides (HEOs), a subcategory of high-entropy ceramics, are becoming an enticing materials platform for a wide range of applications including catalysis, energy storage, and thermoelectric materials, because of increased stability and unexpected properties arising from lattice distortions and cocktail effects between multiple cations.

HEOs are primarily synthesized by the solid-state method, where there is little control over morphology, porosity, and particle size.  As the field of high-entropy oxides is expanding into a wide range of applications, synthesis strategies that can control these physical properties are needed. In this work, we utilize wet synthesis techniques (hydrothermal and co-precipitation) to first make high-entropy precursors with tailored properties which then can be calcined into high-entropy oxides.

In this work, two precursors, high-entropy layered double hydroxide and high-entropy dawsonite-type structure, have been developed and systematically synthesized for chemistry containing 5 or more cations.  Special attention is given to the dawsonite-type structure (NH4M(OH)2CO3)  and its adaptation to a high-entropy form. Specifically, the cations investigated where combinations of Al, Mg, Cr, Fe, Co, Zn, Cu, Ni, Ga, In, Y, Ho, Er, and Ce. The chemistry of high-entropy dawsonite-type materials can be tailored by selecting a wide range of cations and cations sizes, and was able to access chemistries previously not available for dawsonite-type structures.

Finally, these two precursors are shown to calcine to a high-entropy spinel oxide structure and maintain the chemistry, morphology, as well as, porosity from their high-entropy precursors.

The expansion of high-entropy materials to include high-entropy precursors like dawsonite-type structures and layered double hydroxide represents an important step in the development of high-entropy materials targeted for specific catalytic applications and for ceramic powder synthesis, thanks to these materials' porosity and tailorable surface and bulk chemistry