Electronic structure of hole-doped Co-Fe cyanides: Na1.60-δCo[Fe(CN)6]0.90•2.9H2O (0.0≤δ≤0.85)

Lattice, magnetic, and optical properties are investigated for films of Prussian-blue-type cyanides, Na1.60-delta Co[Fe(CN)(6)](0.90)center dot 2.9H(2)O (0.0 <=delta <= 0.85), as a function of hole concentration delta of the d-electron system. The mother compound (delta=0) takes the Co2+ (t(2g)(5)e(g)(2):S=3/2)-Fe2+ (t(2g)(6):S=0) configuration, and the holes are selectively introduced on the Co site. We found that effective magnetic moment mu(eff) decreases with delta, indicating that the Co3+ ion takes a low-spin state (t(2g)(6):S=0). Visible absorption spectra are dominated by three absorption bands at approximate to 2.2 eV, approximate to 3.3 eV, and approximate to 3.8 eV, which are ascribed to charge transfer from Fe2+ to Co3+ sites, CN- to Fe2+ sites, and CN- to Co3+ sites, respectively. Based on these assignments, we proposed an electronic structure model. We further comprehensively discuss variation in the electronic structure with change in the transition-metal site.