Influence of Production Conditions on Thermoelectric Properties of n-Bi₂Te_2.4Se_0.6 Doped with Hg₂Cl₂

Bismuth telluride and compounds based on it are the basic materials for the production of thermocouples p- and n-type operating at low temperatures. Products based on these are commercially mass-produced. In order to improve the thermoelectric characteristics of materials and increase the efficiency of products, it is necessary to make changes to a well-established technological process, which can be associated with significant difficulties. Therefore, relevant is the task of improving the thermoelectric figure of merit of bismuth telluride with minimal changes in the technological process of obtaining it. One option to solve it is to optimize the process parameters of hot pressing. The paper studies the influence of the parameters of the hot-pressing process (pressing pressure and holding time under pressure) on the thermoelectric properties of n-type Bi₂Te₂.₄Se_0.6 solid solution doped with Hg₂Cl₂ calomel. We have obtained the samples using powder metallurgy technology, including synthesis of the material, followed by hot pressing. An increase in the exposure time of a sample under pressure during hot pressing is found to lead to a significant change in electrical properties due to an increase in the concentration of charge carriers and their mobility: the coefficient of thermo-emf decreases on average by 3.5%, electrical conductivity increases by more than 12%. In this case, the thermal conductivity practically does not change, since the increase in the electronic component of thermal conductivity associated with an increase in the concentration of charge carriers is compensated by a decrease in the phonon component. As a result, thermoelectric figure of merit increases by 3.7%. Increasing the dwell time with a simultaneous increase in the compacting pressure increases only charge carrier mobility, their concentration does not change. Therefore, the thermo-emf coefficient remains unchanged, the electrical conductivity increases by 3.0%. Thermal conductivity decreases by 5.3%, due to a slight change in the electronic component (in comparison with the previous production mode) with a significant decrease in the phonon component. As a result, thermoelectric figure of merit increases by 10.0%. Thus, the conditions for the production of n-type bismuth tellurides significantly affect their thermoelectric properties, the selection of the optimal hot-pressing mode allows us increasing the thermoelectric figure of merit without changing the main stages of the technological cycle.

1. RIF – Thermoelectric generators E-resource – Available on: www.rifcorp.ru/products/termoelektricheskiegeneratory (11.7.2019.) (in Russ).

2. Kriotherm – Thermoelectric generator GTEG Eresource – Available on: kryothermtec.com/ru/thermoelectric-generator-gteg.html (11.7.2019.) (in Russ).

3. Thermointech – Thermoelectric generator for the oil and gas industry E-resource – Available on: thermointech.ru/products/generator-termoelektricheskiygte (11.7.2019.) (in Russ).

4. Goltsman B.M., Kudinov B.A., Smirnov I.A. Thermoelectric Semiconductor Materials Based on Bi2Te3 (Poluprovodnikovyye termoelektricheskiye materialy na osnove Bi2Te3). Moscow: Nauka Publ., 1972; 320 p. (in Russ.).

5. Eibl O., Nielsch K., Peranio N., Volklein F. Thermoelectric Bi2Te3 nanomaterials, Wiley–VCH, 2015; 317 p.

6. Maciá-Barber E. Thermoelectric Materials: Advances and Applications. CRC Press, 2015; 364 p.

7. Rowe D.M. Thermoelectrics. CRC Press, 1995; 701 p.

8. Riffat S., Ma X. Thermoelectrics: a Review of Present and Potential Applications. Applied Thermal Engineering, 2003;23:913–935.

9. Heremans J.P. Low-Dimensional Thermoelectricity. Acta Physica Polonica A, 2005;108(4):609–634.

10. Ezzahri Y., Zeng G., Fukutani K., Bian Z., Shakouri A.A. Comparison of Thin Film Microrefrigerators Based on Si/SiGe Superlattice and Bulk SiGe. J. Microelectronics, 2008;39(7):981–991.

11. Venkatasubramanian R., Siivola E., Colpitts T., Quinn B.O. Thin-film Thermoelectric Devices with High Room-temperature Figures of Merit. Nature, 2001;431:597–602.

12. Venkatasubramanian R., Colpitts T., Watko E., Lamvik M., El-Masry N. MOCVD of Bi2Te3, Sb2Te3 and Their Superlattice Structures for Thin-film Thermoelectric Applications. Journal of Crystal Growth, 1997;170:721–817.

13. Funahashi R., Matsubara I. Thermoelectric properties of Pband Ca-doped (Bi2Sr2O4)xCoO2 whiskers. Appl. Phys. Lett, 2001;79(3):362–365.

14. Bulat L.P., Pshenaĭ-Severin D.A. Effect of tunneling on the thermoelectric efficiency of bulk nanostructured materials. Physics of the Solid State, 2010;52(3):485–492.

15. Lin H. et al. Nanoscale clusters in the high performance thermoelectric AgPbmSbTem+2. Phys. Rev. B., 2005;72(174113):1–7.

16. Harman T., Taylor P., Walsh M., LaForge B. Quantum Dot Superlattice Thermoelectric Materials and Devices. Science, 2002;297:2229–2232.

17. Tavkhelidze A. Large enhancement of the thermoelectric figure of merit in a ridged quantum well. Nanotechnology, 2009;20(405401):6.

18. Boukai A. et al. Silicon Nanowires as Efficient Thermoelectric Materials. Nature Letters, 2008;451:168–171.

19. Hochbaum A. et al. Enhanced Thermoelectric Performance of Rough Silicon Nanowires. Nature Letters, 2008;451:163–167.

20. Keyani J., Stacy A.M. Assembly and Measurement of a Hybrid Nanowire-bulk Thermoelectric Device. Appl. Phys. Lett., 2006;89:233106.

21. Shevelkov A.V. Chemical aspects of the design of thermoelectric materials. Russ Chem Rev, 2008;77(1):1–19.

22. Trawinski B. et al. Structure and thermoelectric properties of bismuth telluride-Carbon composites. Materials Research Bulletin, 2018;99:10–17.

23. Bark H., Kim J.S., Kim H., Yim J.H., Lee H. Effect of multiwalled carbon nanotubes on the thermoelectric properties of a bismuth telluride matrix. Current Applied Physics, 2013;13:S111–S114.

24. Kulbachinskii V.A., Kytin V.G., Blank V.D., Buga S.G., Popov M.Yu. Thermoelectric properties of bismuth telluride nanocomposites with fullerene. Semiconductors, 2011;45:1194.

25. Ivanova L.D. et al. Thermoelectric Properties of Bi2Te2.4Se0.6 Solid Solutions of Different Particle-Size Composition. Semiconductors, 2017;51(8):1002.

26. Drabkin I.A. et al. Thermoelectric properties of a material based on (Bi, Sb)2Te3 obtained by spark plasma sintering (Termoelektricheskiye svoystva materiala na osnove (Bi,Sb)2Te3, poluchennogo metodom iskrovogo plazmennogo spekaniya). Electronic Materials, 2012;(3):18–21 (in Russ.).

27. Bhame S.D., Pravarthana D., Prellier W., Noudem J.G. Enhanced thermoelectric performance in spark plasma textured bulk n-type BiTe2.7Se0.3 and p-type Bi0.5Sb1.5Te3. Appl. Phys. Lett., 2013;102(21):211901.

28. Xie W. et al. High performance Bi2Te3 nanocomposites prepared by single-element-meltspinning spark-plasma sintering. J Mater Sci, 2013;48(7):2745–2760.

29. Hu L.P. et al. Improving thermoelectric properties of n-type bismuth–telluride-based alloys by deformation-induced lattice defects and texture enhancement. Acta Materialia, 2012;60(11):4431–4437.

30. Zhai R. et al. Enhancing Thermoelectric Performance of n-type Hot Deformed Bismuth-TellurideBased Solid Solutions by Non-stoichiometry Mediated Intrinsic Point Defects. ACS Appl. Mater. Interfaces, 2017;9(34):28577–28585.

31. Kim D.H., Kim Ch., Heo S.H., Kim H. Influence of powder morphology on thermoelectric anisotropy of spark-plasma-sintered Bi–Te-based thermoelectric materials. Acta Materialia, 2011;59(1):405–411.

32. Han M.K., Jin Y., Lee D.H., Kim S.J. Thermoelectric Properties of Bi2Te3: CuI and the Effect of Its Doping with Pb Atoms. Materials, 2017;10(11):1235.

33. Ge Z.H., Ji Y.H., Chong X., Feng J., He J. Enhanced thermoelectric properties of bismuth telluride bulk achieved by telluride-spilling during the spark plasma sintering process. Scripta Materialia, 2018;143:90–93.

34. Stilbans L.S. Semiconductor Physics (Fizika poluprovodnikov), Moscow: Sovetskoye radio Publ., 1967; 452 p. (in Russ).

35. Ioffe A.F. Physics of semiconductors. New York, Academic Press, 1960; 436 p.

36. Anselm A.I. Introduction to semiconductor theory (Vvedeniye v teoriyu poluprovodnikov). Moscow: Nauka Publ., 1978; 616 p. (in Russ).

37. Hao F. et al. High efficiency Bi2Te3-based materials and devices for thermoelectric power generation between 100 and 300 ºC. Energy Environ. Sci., 2016;9(10):3120–3127.

38. Sheng S.L. Semiconductor physical electronics.Springer, 2006; 697 p.

39. Tritt T.M. Thermoelectric Phenomena, Materials and Applications. Annu.Rev.Mater.Res., 2011;41:433–448.

40. Snyder G. Complex thermoelectric materials. Nature Materials, 2008;7:105–114.

41. Belonogov E.K. Effect of photon treatment on structure and substructure of Bi2Te3–хSeх thermoelectric material (Vliyaniye fotonnoy obrabotki na strukturu i substrukturu termoelektricheskogo materiala Bi2Te3–хSeх). Perspektivnyye materialy, 2019;(12):31–38 (in Russ).