Insight into the local coordination environment of water to sodium in Prussian White using neutron total scattering

Prussian Blue Analogues (PBAs) are an interesting class of material to use as cathode material in Na-ion batteries, in particular, the Fe-based vacancy-free Na-rich PBA, known as Prussian White (PW, Na2Fe[Fe(CN)6]·zH2O), is a promising candidate. PW exhibits a near room temperature phase transition from P21/n to R-3, which is due to an octahedral tilt transition. In the P21/n model, the water is randomly distributed in a plane, while the ordering of the water is lost when transforming to the R-3 structure. Thus, we propose a neutron total scattering experiment to determine the position of water and the local coordination environment of Na in both room temperature structures as it was not possible from the average structures. The results will aid the understanding of the origin of the octahedral tilt transitions and the role that water plays in these tilt transitions in PW.