Abstract
The chemical substitution of a transition metal (M) is an effective method to improve the functionality of materials. In order to design the highly functional materials, we first have to know the local structure and electronic state around the substituted element. Here, we systematically investigated the local structure and electronic state of the host (Mh) and guest (Mg) transition metals in metal-hexacyanoferrate (M-HCF), Nax(Mh, Mg)[Fe(CN)6]y (1.40 < x < 1.60 and 0.85 < y < 0.90), by means of extended X-ray absorption fine structure (EXAFS) and X-ray absorption near-edge structure (XANES) analyses. The EXAFS and XANES analyses revealed that the local structure and electronic state around Mg are essentially the same as those in the pure compound, i.e, Mg-HCF. Such an invariant nature of Mg in M-HCF is in sharp contrast with that in layered oxide, in which the Mg valence changes so that local Mg-O distance (dM-Og) approaches the Mh-O distance (dM-Oh).
Highlights
By means of the systematic EXAFS and X-ray absorption near edge structure (XANES) analyses, we found that the local structure and electronic state of Mg in M-HCF are essentially the same as those in the pure material, i.e., Mg-HCF
Such an invariant nature observed in M-HCF is in sharp contrast with the layered oxide systems
Our observation indicates that M-HCF is a novel platform of transition metals, in which magnetic, electronic, local structural properties of them are the same as those in the pure compound
Summary
We performed careful EXAFS analysis on three pure (M-HCF) and six mixed (MhMg-HCF) compounds. Details of synthesis and characterization are described in the Method section. In the EXAFS analyses, we included the contributions from the first(N) and second- (C) nearest neighbor elements. In order to include the Fe(CN)[6] vacancy effect, the coordination numbers (NN) of N are treated as an adjustable parameter with restriction of NN + NO = 6 and dM-O = dM-N, where No is the coordination number of O. With use of the EXAFS equation, least-squares fittings are performed for the FT[χ(k)k3]−R plots (Fig. S2).
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