First-Principles Study of Electronic Structure and Thermoelectric Properties for Guest Substituted Clathrate Compounds Ba₆R₂Au₆Ge₄₀ (R=Eu or Yb)

Abstract

The electronic structure and thermoelectric properties of guest substituted clathrate compounds Ba₆R₂Au₆Ge₄₀ (R=Eu, Yb) are calculated using the full-potential linearized augmented plane wave method based on the density functional theory. The bottom of conduction band for Ba₈Au₆Ge₄₀ is formed by one relativity dispersive band close to the M point. When the Ba 2a site is replaced by Eu and Yb, the lowest conduction bands at X point shift to lower energy side. The coupling between gusest atom at 2a sites and the host framework becomes weaker with decreasing ionic radii. This multivalley effect in M and X points yields the increase in the density of states near the conduction band edge, resulting in the increase in the Seebeck coefficient for n-type doping. On the other hand, the valence band edge is almost independent of the guests; the f-bands of Eu and Yb are narrow and distant from the band edge. The effect of Eu and Yb substitution on the Seebeck coefficient is small for p-type doping at higher temperature.