Dependence of the crystal structure of Prussian blue on the occupation of interstitial sites

Transition metal ferrocyanide compounds, widely known as Prussian blue analogues (PBAs), constitute a class of metal-organic frameworks (MOFs) that exhibit a broad spectrum of physical properties and technological applications. Recently, PBAs have garnered significant attention as promising cathode materials for lithium-free rechargeable batteries. In this study, we present a comprehensive investigation, based on density functional theory (DFT), into the crystal structure and alkali-ion site occupancy of two representative systems: Prussian blue (AFe[Fe(CN)₆]) and Prussian white (A₂Fe[Fe(CN)₆]), both in their soluble and insoluble forms, under various alkali-metal intercalations (A = Li⁺, Na⁺, K⁺, Rb⁺). Our combined theoretical and experimental analysis reveals that the resulting crystal structure is governed primarily by the amount of alkali ion intercalation and the preferred occupancy sites within the lattice, rather than the specific identity of the intercalated alkali species. Finally, the computational findings are critically compared with experimental data from electrodeposited KFe[Fe(CN)₆] and K₂Fe[Fe(CN)₆] samples, highlighting the consistency between theoretical predictions and observed structural configurations.