The higher anion vacancy content in KFeRT than KFe60 can be indicated by the more irregular shape of the nanoparticles in the former than the latter. TEM images (Figures and) further reveal the irregular shapes of the primary nanoparticles and their agglomeration. Highresolution TEM (HRTEM) images (insets in Figures and) display clear lattice fringes in both samples. The d spacings of 0.343 nm for KFeRT and 0.279 nm for KFe60 correspond to the diffraction planes of (120) and (311), respectively. The different d spacings are due to the non-uniformly oriented growth of the primary nanoparticles in the samples; nevertheless, the crystalline nature of the nanoparticles can be confirmed. Our compositional and structural analysis reveal that KFeRT and KFe60 have similar structures and non-stoichiometric compositions that contain [Fe(CN)6] 4-anion vacancy, and a lower precipitation temperature leads to a higher vacancy content 7 in KFeRT being ~3 times higher than KFe60 (20% vs. 7%).