Evolution of water dynamics in the Prussian blue

Abstract

Crystal water plays a crucial role towards the multifunctional properties of Prussian blue and its analogue (PBA) compounds. We have investigated the dynamics of crystal water in Prussian blue (PB), Fe(III)4[Fe(II)(CN)6]3. 14H2O using Quasielastic Neutron Scattering (QENS). In PB, water molecules exist in the spherical cavity, created due to the vacant sites of Fe(CN)6 units, and also at interstitial sites. QENS data showed that dynamics evolves with increase in temperature. The observed dynamics has been correlated quantitatively with the different water molecules that exist at different sites of the lattice. It is found that only the non-coordinated water molecules contribute to the dynamics at low temperature, and others start contributing progressively with increasing temperature. A detailed data analysis showed that the water molecules undergo a localized translational diffusion. The estimated spatial domain of dynamics is found to be compatible with the geometry of the structure.