Thermoelectric properties of Ba-filled Si-Ge alloy type I semiconducting clathrates

We report the synthesis of the Si-Ge alloy type I clathrate Ba₈Ga₁₆Si_xGe_30-x including a systematic investigation of the electrical properties by varying the Si-to-Ge ratio while a constant Ga-to-group IV element ratio is maintained. These Si-Ge type I clathrate samples demonstrate transport properties in direct contrast to those expected in a typical rigid band semiconducting material. The increasing Si substitution correlates to an increase in |S| even as the resistivity decreases and the carrier concentration increases, suggesting a modified band structure as compared to Ba₈Ga₁₆Ge₃₀. The structural, chemical, and electrical transport properties of Ba₈Ga₁₆Si_xGe_30-x are reported in comparison to Ba₈Ga₁₆Ge₃₀ and Sr₈Ga₁₆Si_xGe_30-x.