Large thermoelectric power factor at low temperatures in one-dimensional telluride Ta4SiTe4

Abstract

We report the discovery of a very large thermoelectric power over 400 V K 1 in the whisker crystals of a one-dimensional telluride Ta 4 SiTe 4 , while maintaining a low electrical resistivity of  = 2 mcm, yielding a very large power factor of P = 80 W cm 1 K 2 at an optimum temperature of 130 K. This temperature is widely controlled from the cryogenic temperature of 50 K to room temperature by chemical doping, resulting in the largest P of 170 W cm 1 K 2 at 220-280 K. These P values far exceed those of the Bi 2 Te 3 -Sb 2 Te 3 alloys at around room temperature, offering an avenue for realizing the practical-level thermoelectric cooling at low temperatures. The coexistence of a one-dimensional electronic structure and a very small band gap appearing in the vicinity of the Dirac semimetals probably causes the very large power factors in Ta 4 SiTe 4 , indicating that the "one-dimensional Dirac semimetal" is a promising way to find high-performance thermoelectric materials for the low temperature applications.

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

“…The largest P of the p-type M4SiTe4 is realized in (Nb0.95Ti0.05)4SiTe4, which shows a maximum value of Pmax = 57 W cm −1 K −2 at the optimum temperature of 210 K. Pmax values of (Nb0.99Ti0.01)4SiTe4 and (Ta0.95Ti0.05)4SiTe4 are also larger than the 35 W cm −1 K −2 for Bi2Te3-based materials. 16,17 These power factors are smaller than Pmax = 170 W cm −1 K −2 in the n-type sample, 12 but exceed the practical level in the wide temperature range from 130 to 270 K, indicating that the p-type M4SiTe4 samples prepared in this study have high enough performance to be combined with the n-type ones in a thermoelectric device. The large power factor of p-type M4SiTe4 is expected to be related to its characteristic band structure with a very small band gap and strongly onedimensional band dispersion, as in the case of n-type M4SiTe4.…”

“…The data for undoped Ta4SiTe4 are also shown as a reference. 12 Although the undoped Ta4SiTe4 shows negative S below room temperature, only 0.1 % Ti doping results in positive S between 50 and 250 K. S of the x = 0.001 sample is negative below 50 K, strongly increases at around 50 K with increasing temperature, and then shows a maximum value of S = 560 V K −1 at 90 K. This S far exceeds the maximum |S| of ~400 V K −1 in undoped Ta4SiTe4, indicating that this system is also promising as a ptype material. Further increases in temperature lead to gradual and then strong decreases in S, resulting in negative S once again above 250 K. On the other hand,  of the x = 0.001 sample is more than an order of magnitude larger than that of the undoped one.…”

“…The large power factor of p-type M4SiTe4 is expected to be related to its characteristic band structure with a very small band gap and strongly onedimensional band dispersion, as in the case of n-type M4SiTe4. 12,15 Here we discuss the thermoelectric properties of p-type M4SiTe4, mainly by using experimental data for (Ta0.999Ti0.001)4SiTe4, where the thermally activated behavior is most clearly observed. As shown in the Arrhenius plot of the electrical conductivity ( = 1/) of (Ta0.999Ti0.001)4SiTe4 shown in Fig.…”

Giant enhancement of cryogenic thermopower by polar structural instability in the pressurized semimetal MoTe2

“…In the cryogenic temperatures below 50 K, strongly correlated electron systems such as cobalt oxides and heavy-fermion compounds [1-5] were found to show much larger power factors than those for high-mobility semiconductors and semimetals typified by Bi2Te3 (see Fig. 4) [6][7][8][9][10].Since thermopower is the measure of the entropy normalized per charge carrier, the unusually high power factors originated from the high thermopower in these compounds were discussed in terms of the large entropy of spin and orbital degrees of freedom.As well as the spin and orbital entropy, the phonon entropy has a potential for the enhancement of thermopower through electron-phonon scattering [11,12]. A typical example is the phonon-drag effect observed in the clean system with long mean free path phonons [12].…”

Large thermoelectric power factor in one-dimensional telluride Nb4SiTe4 and substituted compounds

“…Recently, whisker crystals of the one-dimensional telluride Ta 4 SiTe 4 and its substituted compounds were found to show high thermoelectric performances at low temperatures. 1 Their whisker form is typically several mm long and several m in diameter, reflecting the strongly one-dimensional crystal structure comprising Ta 4 SiTe 4 chains. 2,3 The electrical resistivity  and thermoelectric power S data measured along the whiskers, i.e.…”