Thermoelectric properties of the incommensurate layered semiconductor Ge_xNbTe₂

The compounds Ge_xNbTe₂ (0.39≤x≤0.53) have been studied for their thermoelectric properties. By changing x, the carrier concentration can be adjusted so that the material changes from a p-type metal to a p-type semiconductor. The maximum germanium concentration at about Ge_0.5NbTe₂, is also the most semiconducting composition. High and low temperature electrical resistivity, Hall effect, Seebeck coefficient, and thermal conductivity were measured. The thermal conductivity is reasonably low and glass-like with room temperature values around 20-25 mW/cm K. However, the power factor is too low to compete with state of the art materials. The maximum ZT found in these compounds is about 0.12. The low ZT can be traced to the low carrier mobility of about 10 cm²/Vs. The related compounds Si_0.5NbTe₂ and Ge_0.5TaTe₂ were also studied.