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

We report the synthesis of the Si-Ge alloy type I clathrate Ba/sub 8/Ga/sub 16/Si/sub x/Ge/sub 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 Ba/sub 8/Ga/sub 16/Ge/sub 30/. The structural, chemical, and electrical transport properties of Ba/sub 8/Ga/sub 16/Si/sub x/Ge/sub 30-x/ are reported in comparison to Ba/sub 8/Ga/sub 16/Ge/sub 30/ and Sr/sub 8/Ga/sub 16/Si/sub x/Ge/sub 30-x/.