A solution-based route to compositionally complex metal oxide structures using high-entropy layered double hydroxides

Although complex metal oxides with tailored compositions are increasingly in demand for applications in advanced technologies, their preparation by solution-based routes, which are typically low cost and easy to scale up, is challenging. Here, we report high-entropy layered double hydroxides (HE-LDHs) having complex compositions as precursors for complex metal oxides. Furthermore, we reveal that the ionic radii are the key factors determining the incorporation of the metal cations into the hydroxide layers, which can contain up to 10 different kinds of metal cations simultaneously having a metal cation ratio inherited from the reaction solution. Furthermore, spinel-based complex oxides can be prepared by heat treating the HE-LDHs in air, and their metal cation ratios are maintained over expansive heat-treatment temperatures (up to 1,200°C). Therefore, the results reveal that complex oxides with tailored compositions can be prepared using solution-based approaches, enabling the large-scale fabrication of oxides with precisely controlled physicochemical properties for various applications.