Electronic structure of hole-doped transition metal cyanides

Electronic structures of hole-doped transition metal cyanides, Na0.84-xCo[Fe(CN)6]0.71·3.8H2O (NCF71), Na0.72-xNi[Fe(CN)6]0.68·5.1H2O (NNF68) and Na1.60-xCo[Fe(CN)6]0.90·2.9H2O (NCF90), were investigated by means of the x-ray absorption spectroscopy and the valence differential spectroscopy. The x-ray absorption spectroscopy revealed that the holes are introduced on the Fe, Fe, and Co sites for the NCF71, NNF68 and NCF90 films, respectively. Owning to the valence differential spectroscopy, we unambiguously assigned the spectral components to the respective optical transitions. We further found that an ab initio band calculation based on the local density approximation with the on-site Columbic repulsion (LDA+U) semi-quantitatively explains the optical transitions. (author)