researchers at nagoya university (japan) have developed one-dimensional crystalline compounds, composed of tantalum, silicon, and tellurium, which have a wide range of thermoelectric powers from cryogenic levels (around -223°c) up to room temperature while also maintain low electrical resistivity.

ta4site4 whisker crystals (left lower) show very large thermoelectric power exceeding -
400 μv k-1 at low temperature, while maintaining low electrical resistivity.
(nagoya university)

according to report on the university website, the samples that the researchers used in experiments included pure ta₄site₄ as well as crystals that had low levels of molybdenum and antimony added in order to test the impact on thermal conductivity and thermoelectric power.

the article explained, “addition of as little as 0.1% molybdenum doping caused the resistivity of the telluride-type crystals to decrease dramatically at low temperatures, while they also demonstrated high thermoelectric powers that were closely related to the strongly one-dimensional electronic structures of the materials.”

it added, “the power factors of the crystals at room temperature greatly exceeded the corresponding values of the conventional bi₂te₃-based alloys that are commonly used in thermoelectric applications, and these crystals thus represent a highly promising route towards the development of high-performance thermoelectric cooling solutions at very low temperatures.”

the work was recently published in applied physics letters. the abstract stated:

“we report the discovery of a very large thermoelectric power over –400 μv k⁻¹in the whisker crystals of a one-dimensional telluride ta₄site₄, while maintaining a low electrical resistivity of ρ = 2 mω cm, yielding a very large power factor of p = 80 μw cm⁻¹k⁻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 μw cm⁻¹k⁻² at 220–280 k. these p values far exceed those of the bi₂te₃-sb₂te₃ 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 ta₄site₄, indicating that the ‘one-dimensional dirac semimetal’ is a promising way to find high-performance thermoelectric materials for the low temperature applications.”