Thermoelectric properties of silicon-germanium type I clathrates

We report the synthesis and chemical, structural, and transport properties characterization of Ba8Ga16SixGe30-x type I clathrates with similar Ga-to-group IV element ratios but with increasing Si substitution (4 < x < 14). Substitution of 20 at. % Si within the Ga-Ge lattice framework of the type I clathrate Ba8Ga16Ge30 results in thermoelectric performance enhancement. The unique dependences of carrier concentration, electrical resistivity, Seebeck coefficient, and carrier effective mass on Si substitution level, and the lack of variation in the Ga-to-group IV element ratios may imply a modified band structure with Si substitution. These results indicate an additional method for tuning the electronic properties of Ba8Ga16Ge30 for thermoelectric applications.