Nanocrystalline Precursors for the Co‐Assembly of Crack‐Free Metal Oxide Inverse Opals

Inorganic microstructured materials are ubiquitous in nature. However, their formation in artificial self‐assembly systems is challenging as it involves a complex interplay of competing forces during and after assembly. For example, colloidal assembly requires fine‐tuning of factors such as the size and surface charge of the particles and electrolyte strength of the solvent to enable successful self‐assembly and minimize crack formation. Co‐assembly of templating colloidal particles together with a sol–gel matrix precursor material helps to release stresses that accumulate during drying and solidification, as previously shown for the formation of high‐quality inverse opal (IO) films out of amorphous silica. Expanding this methodology to crystalline materials would result in microscale architectures with enhanced photonic, electronic, and catalytic properties. This work describes tailoring the crystallinity of metal oxide precursors that enable the formation of highly ordered, large‐area (mm2) crack‐free titania, zirconia, and alumina IO films. The same bioinspired approach can be applied to other crystalline materials as well as structures beyond IOs.