The efficiency of thermoelectric device is determined by the material's thermoelectric figure of merit ZT=S2σT/κ. Therefore, low thermal conductivity κ is essential to achieve high ZT value. Here we show the high-temperature thermoelectric properties of α-Ag9GaTe6. Polycrystalline high-density bulk samples of α-Ag9GaTe6 were prepared. The sample showed quite low thermal conductivity to be 0.25 W m−1 K−1 at room temperature, corresponding to the mean free path of phonons of around 0.4 nm. α-Ag9GaTe6 exhibited relatively high ZT value of ~0.36, mainly due to the low thermal conductivity.
