Structural and transport properties of Ba8Ga16SixGe30−x clathrates

We report on the structural, chemical, electrical resistivity, Seebeck coefficient, thermal conductivity, and Hall measurements of polycrystalline Si–Ge type-I clathrates with nominal composition of Ba8Ga16SixGe30−x such that a constant Ga-to-group-IV element ratio is maintained while varying the Si-to-Ge ratio. Electrical transport measurements on the n-type specimens show a modest increase in the absolute Seebeck coefficient and a decrease in electrical resistivity with increasing Si content. This may imply a modification in the band structure with Si substitution and reveals a possible approach for optimizing these materials for thermoelectric applications. These data are compared with those of Ba8Ga16Ge30 and Sr8Ga16SixGe30−x.