Thermoelectric properties of Au-containing type-I clathrates Ba ₈Au_xGa_{16-3 x}Ge_30+2x

Type I clathrates, with compositions based on Ba₈Ga ₁₆Ge₃₀, are a class of promising thermoelectric materials due to their intrinsically low thermal conductivity. It has been demonstrated previously that the thermoelectric performance can be improved by transition metal substitution of the framework atoms. In this study, the effects of Au substitution for Ga/Ge on thermal and electrical transport properties of type I clathrate compounds have been investigated. Polycrystalline samples with a large range of Au content have been synthesized using conventional solid state techniques with the actual compositions of resulting materials approximately following Zintl-Klemm rules. The charge carrier type changes from electrons (n) to holes (p) as the Au content increases. The Seebeck coefficient (S) and power factor (S²/ρ where ρ is the electrical resistivity) were improved by Au substitution and the resulting overall thermoelectric properties were enhanced by Au substitution as compared to polycrystalline Ba ₈Ga₁₆Ge₃₀. The thermoelectric figure of merit ZT attains a value of 0.63 at 740 K for the composition Ba₈Au _5.47Ge_39.96, a value that is somewhat lower than those reported previously. The results presented herein show that Au-containing type I clathrates are promising p-type thermoelectric materials for high temperature applications.