  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 uW 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 are not covered by
Bi2Te3-based materials.
