Effect of Deviation from Stoichiometry on Thermoelectric Properties of Bi2Te3 Polycrystals and Thin Films in the Temperature Range 77-300 K

Authors E.I. Rogacheva, K.V. Novak, A.N. Doroshenko, O.N. Nashchekina, A.V. Budnik

National Technical University “Kharkiv Polytechnic Institute”, 2, Kyrpychov St., 61002 Kharkiv, Ukraine

Е-mail rogachova.olena@gmail.com
Issue Volume 11, Year 2019, Number 5
Dates Received 22 July 2019; revised manuscript received 22 October 2019; published online 25 October 2019
Citation E.I. Rogacheva, K.V. Novak, A.N. Doroshenko, et al., J. Nano- Electron. Phys. 11 No 5, 05027 (2019)
DOI https://doi.org/10.21272/jnep.11(5).05027
PACS Number(s) 72.20.My, 72.20.Pa
Keywords Bi2Te3 (3) , Stoichiometry (2) , Electrical conductivity (10) , Seebeck coefficient, Hall coefficient, Charge carrier mobility, Temperature dependences.

Bi2Te3 semiconductor compound and Bi2Te3-based solid solutions are presently among the best low-temperature thermoelectric materials. One of the methods of controlling the conductivity type and properties of Bi2Te3 is changing the stoichiometry of this compound. Earlier, we have obtained the room-temperature dependences of mechanical and thermoelectric properties of Bi2Te3 polycrystals on the degree of deviation from stoichiometry. The goal of this work is to investigate the behavior of such dependences at other temperatures. Bismuth telluride polycrystals with compositions in the range of 59.6-67.5 at. % Te were obtained, and for all the crystals the Seebeck coefficient, the Hall coefficient, electrical conductivity and charge carrier mobility were measured in the temperature range 77-300 K. On the basis of the temperature dependences, the isotherms of kinetic coefficients were plotted. It was found that similar to the room-temperature isotherms, the isotherms at lower temperatures were non-monotonic: they exhibited inversion of the conductivity sign between 60.5 and 61.0 at. % Te and extrema near 60.0 and 63.0 at. % Te. The experimental data are interpreted taking into account changes in the band and defect structures of Bi2Te3 under varying stoichiometry. The obtained results make it possible to control thermoelectric properties of Bi2Te3 polycrystals in the temperature range 77-300 K by changing the degree of deviation from stoichiometry.

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