Characterization of Prussian Blue analogue: nanocrystalline nickel-iron cyanide

Characterization of nanocrystalline nickel-iron cyanide was carried out from the viewpoints of composition, electrical conductivity, crystal parameters, and model of crystal structure. The nickel-iron cyanide was synthesized by mixing two solutions containing nickel (II) and hexacyanoferrate (III) ions, respectively. The soluble form with potassium and the insoluble form without potassium were obtained by changing the mixing ratio of nickel/iron in the starting solutions. The representative composition of the insoluble form was determined to be Ni(II)4[Fe(III)(CN)6]8/3 · 17H2O. The electrical conductivity was of the order of 10−5 S·m−1 at room temperature. The crystal phase was an NaCl-type cubic with the unit cell of 1.022 nm and the average crystallite size of 12.9 nm. The structure model in which nickel and iron statistically located at vacant sites was proposed, where water molecules in the lattice also exerted influence on simulation of the X-ray diffraction (XRD) pattern.