Hole-doped M₄SiTe₄ (M = Ta, Nb) as an efficient p-type thermoelectric material for low-temperature applications

Solid-state thermoelectric cooling is expected to be widely used in various cryogenic applications such as local cooling of superconducting devices. At present, however, thermoelectric cooling using p- and n-type Bi₂Te₃-based materials has been put to practical use only at room temperature. Recently, M₄SiTe₄ (M = Ta, Nb) has been found to show excellent n-type thermoelectric properties down to 50 K. This paper reports on the synthesis of high-performance p-type M₄SiTe₄ by Ti doping, which can be combined with n-type M₄SiTe₄ in a cooling device at low temperatures. The thermoelectric power factor of p-type M₄SiTe₄ reaches a maximum value of approximately 60 μW cm⁻¹ K⁻² at 210 K and exceeds the practical level in a wide temperature range of 130–270 K. A finite temperature drop by Peltier cooling was also achieved in a cooling device made of p- and n-type Ta₄SiTe₄ whisker crystals. These results clearly indicate that M₄SiTe₄ is promising to realize a practical thermoelectric cooler for use at low temperatures, which is not covered by Bi₂Te₃-based materials.