Preparation and thermoelectric properties of sintered iodine-containing clathrate compounds Ge38Sb8I8 and Sn38Sb8I8

The iodine-containing cationic type-I clathrates Ge₃₈Sb₈I₈ and Sn₃₈Sb₈I₈ were prepared and their thermodynamic properties as well as their thermoelectric properties were investigated. Their atomic displacement parameters were as large as those of anionic clathrates such as Ba₈Ga₁₆Ge₃₀ and Cs₈Cd₄Sn₄₂. The room temperature thermal conductivities of Ge₃₈Sb₈I₈ and Sn₃₈Sb₈I₈ were 7 and 12mWcm^-1K^-1, respectively; these values were as low as that of the above anionic clathrates. Both cationic clathrates had negative Seebeck coefficients; the band gap energies of Ge₃₈Sb₈I₈ and Sn₃₈Sb₈I₈ were 1.16 and 0.80eV, respectively.