Thermoelectric figure of merit semimetal and semiconductor Bi1–xSbx alloy foils
A. Nikolaeva1,2, L. Konopko1,2, I. Ghergishan1, K. Rogacki2, P. Stachowiak2, A. Jeżowski2, V. Shepelevich3, V. Prokoshin3, and S. Gusakova3
1Ghitu Institute of Electronic Engineering and Nanotechnologies, A.S.M., Academiei str., 3/3, MD-2028, Chisinau, Republica Moldova
2Institute of Low Temperatures and Structure Research, Wroclaw, Poland
3Belarusian State University, Minsk, Belarus
Received December 21, 2017, revised January 30, 2018
Temperature dependences of thermal conductivity χ(Т), electrical conductivity σ(Т), and thermopower α(Т) in foils of Bi1–xSbx alloys in the semimetal and semiconductor states in a temperature range of 4.2–300 K are experimentally studied. Foils of Bi1–xSbx alloys are prepared by high-speed crystallization of a thin layer of the melt on the polished inner surface of a rotating copper cylinder. High crystallization rates at a level of v = 5·105 m/s provide a uniform distribution of the components in the volume. The foils have a thickness of 10–30 μm, the 101̅2 texture parallel to the foil plane, and the C3 axis coinciding with the normal to the foil surface. It is shown that, in the low-temperature range (T < 10 K), the thermal conductivity of the semimetal (Bi–3 at% Sb) and semiconductor (Bi–16 at% Sb) foils is, respectively, two orders of magnitude and an order of magnitude lower than the thermal conductivity of the bulk samples of the same composition. This effect is interpreted the point of view of the combined additional phonon scattering on both surface and grainboundary of the foil. The ρ(Т), α(Т) and χ(Т) dependences are used to calculate the thermoelectric figure of merit of the foils ZT = α2σ/χ in a temperature range of 5–300 K. It is found that, at 100 K, thermoelectric figure of merit ZT in the semiconductor Bi1–xSbx alloys is 2 times higher than that of the bulk samples of the same composition and crystallographic orientation; this feature can be used in low-temperature thermoelectric energy converters.
PACS: 72.20.Pa Thermoelectric and thermomagnetic effects;
Key words: semiconductor foils, thermoelectricity, topological insulator, dimensional effects, phonon scattering, thermal conductivity.
Published online: June 27, 2018