Electrostatic Control of Electronic Structure in Modular Inorganic Crystals

The rules that govern structure and bonding, established for elemental solids and simple compounds, are challenging to apply to more complex crystals formed of polyatomic building blocks, such as layered or framework materials. Whether these modular building blocks are electrically neutral or charged influences the physical properties of the resulting crystal. Despite the prevalence of alternating charged units, their effects on the electronic structure remain unclear. We demonstrate how the distribution of charged building blocks, driven by differences in the electrostatic potential, governs the electronic band energies formed in layered crystals. This coarse-grained model predicts the spatially separated valence and conduction band edges observed in the metal-oxyhalide Ba₂Bi₃Nb₂O₁₁Cl and explains observed property trends in the Sillén–Aurivillius crystal system. Moreover, the general nature of the model allows for extension to other modular structure types, illustrated for Sillén and Ruddlesden–Popper layered compounds, and can support the rational design of electronic properties in diverse materials.