Thermoelectric properties of Ba-Ge based type-III clathrate compounds

The crystal structures and thermoelectric properties of Ba-Ge based type-III clathrate compounds in Ba-Al-Ge and Ba-In-Ge systems have been investigated as a function of Al and In content. The absolute values of electrical resistivity and Seebeck coefficient increase, while that of lattice thermal conductivity decreases with increasing Al and In content. The increase in electrical resistivity and Seebeck coefficient is discussed in terms of the number of the excess electrons deduced from the Zintl concept, on the other hand, the decrease in lattice thermal conductivity is discussed in terms of an anisotropic deformation of the open-dodecahedron cage encapsulating Ba atom. High ZT values of 0.7 and 0.87 are obtained at 780 and 580 °C for Ba ₂₄Al₁₂Ge₈₈ and Ba₂₄In ₁₆Ge₈₄. respectively.