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Electronic structures of hole-doped transition metal cyanides, Na 0:84Àx Co[Fe(CN) 6 ] 0:71 . 3.8H 2 O (NCF71), Na 0:72Àx Ni[Fe(CN) 6 ] 0:68 . 5.1H 2 O (NNF68) and Na 1:60Àx Co[Fe(CN) 6 ] 0:90 . 2.9H 2 O (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 onsite Columbic repulsion (LDA+U) semi-quantitatively explains the optical transitions.

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A full-potential augmented-plane-wave (FLAPW) band-structure calculation in the local density approximation (LDA) was carried out for hexagonal Na(x)CoO(2) (x = 0.45, 0.55, 0.66 and 0.75). The Seebeck tensor was estimated by the Boltzmann theory, assuming that the relaxation time is constant on the Fermi surface. The Seebeck tensor is extremely anisotropic; the c-axis Seebeck coefficient varies dramatically with the Na content. The calculation reproduces the experiment semiquantitatively.

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We focus on the defect and phase stabilities in the pseudo binary alloy (GeTe) x (AgSbTe 2 ) 1%x (TAGS; tellurium antimony germanium silver). TAGS is expected to be a high effective thermoelectric material because its thermal conductivity shows anomalous behavior around the concentration of x = 0.8. The origin of the anomalous thermal conductivity and the stable structure in TAGS have not been well understood. To clarify the stable structure, we calculate the formation energies of the point and complex defects. It is found that the chain structure of Ag-Te-Sb has a lower formation energy in GeTe, and the system becomes more stable by assembling the Ag-Te-Sb chain structures. Moreover, the calculated mixing energy also shows that the TAGS system tends to undergo phase separation. In such structures, the grain boundary plays an important role in inducing large phonon scattering, leading to the thermal conductivity reduction.

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We theoretically investigate the impurity doping effects on the structural parameters such as lattice constant, atomic positions, and site preferences of impurity dopants for Al-doped magnesium silicide (Mg 2 Si) crystal using the first-principles calculation methods. We present comparison between several codes: ABCAP, Quantum Espresso, and Machikaneyama2002 (Akai KKR), which are based on the full-potential linearized augmented plane-wave method, the pseudopotential method, and KKR/GGA Green's function method, respectively. As a result, any codes used in the present study exhibit qualitative consistency both in the dependence of the lattice constants on the doping concentration and the energetic preference of the Al atom for the following sites; substitutional Si and Mg sites, and interstitial 4b site; in particular, ABCAP, which is based on the all-electron full-potential method, and Quantum Espresso, which is a code of the pseudopotential method, produce closely-resemble calculation results. We also discuss the effects of local atomic displacement owing to the presence of impurities to the structural parameters of a bulk. Using the analytical method considering the local atomic displacement, moreover, we evaluate the formation energy of Na-and B-doped systems as examples of p-type doping in order to examine the possilbility of realizing p-type Mg 2 Si.