Logo: to the web site of Uppsala University

Prussian blue analogues (PBAs), A_xM[M’(CN)₆]_1–y·zG, are used in many different applications, such as energy storage, due to their tunable composition and structural diversity. To understand the material properties, it is important to accurately determine the composition and atomic structure of these materials. However, this is challenging due to the interdependent relationship between the three compositional parameters: the alkali cation (A_x), water (z), and [M’(CN)₆]^n– (y) vacancy content. Furthermore, the atomic structure depends on the composition, which leads to a rich structural landscape that further influences the material properties. This thesis presents a comprehensive strategy for characterizing the composition and atomic structure of iron- and sodium-based PBAs. To accurately determine the composition of iron-based PBAs, it was found that a combination of multiple characterization techniques is needed; especially Mössbauer spectroscopy proved vital for accurately determining the vacancy content. Neutron diffraction, neutron total scattering, quasi-elastic neutron scattering, and inelastic neutron scattering were applied to probe the local and average structures as well as the dynamics of the water in PBAs as a function of sodium content and temperature. It was found that the PBA system is more dynamic than previously thought, and that the sodium and water can occupy a broad range of positions, which change with temperature. The material becomes more disordered upon dehydration or when the sodium content is lowered. Additionally, distortions of the PBA framework proved to be an inherent property of these materials. This work also demonstrates that neutron diffraction alone is insufficient to describe sodium and water positions, confirming the need for local probes such as total scattering and inelastic neutron scattering. These findings highlight the importance of proper compositional, structural, and dynamical characterization using multiple techniques and lay the groundwork for further development of new PBAs.