Doubled Thermoelectric Figure of Merit in p-Type β-FeSi₂ via Synergistically Optimizing Electrical and Thermal Transports

Abstract

β-FeSi2 has long been investigated as a promising thermoelectric (TE) material working at high temperatures due to its combining features of environmental friendliness, good thermal stability, and strong oxidation resistance. However, the real application of β-FeSi2 is still limited by its low TE figure of merit (zT). In this study, nearly doubled zT in p-type β-FeSi2 has been achieved via synergistically optimizing electrical and thermal transports. Based on the first-principles calculations, Al with shallow acceptor transition level and high carrier donation efficiency is chosen to dope β-FeSi2. Significantly improved electrical transport, particularly in the low temperature range, has been obtained in the Al-doped β-FeSi2 system. The power factor for FeSi1.96Al0.04 at 300 K is even higher than that of p-type β-FeSi2-based compounds reported previously at high temperatures. By alloying β-FeSi2 with Os at the Fe sites, we further lower the lattice thermal conductivity. Fe0.80Os0.20Si1.96Al0.04 possesses the lowest lattice thermal conductivity among the β-FeSi2 compounds prepared by the equilibrium method. Finally, a record-high zT value of 0.35 is obtained for p-type Fe0.80Os0.20Si1.96Al0.04. This study is expected to accelerate the application of β-FeSi2.

Effect of Nanostructuring on the Thermoelectric Properties of β-FeSi2

“…These low ZT values are mainly related to the high value of λ Tot which is about 6.2 W/mK or 4.3 W/mK at 300 K for Al or Co alloying, respectively [7]. Recently, alloying with both Al and up to 20% of Os leads to an increase in the ZT of p-type β-FeSi 2 up to 0.35 [15]. However, the use of Os is expensive and its oxide is very toxic and will limit its applications.…”

Exceptionally Heavy Doping Boosts the Performance of Iron Silicide for Refractory Thermoelectrics

“…Toward the application in industrial kilns, it becomes the compelling obligation to develop refractory high‐performance TE materials that synergistically possess high oxidation resistance, high thermal and chemical stability (in both crystal structure and microstructure), and high zT at elevated temperatures. In actuality, in the existing TE families, only oxides [ 28 ] and β‐FeSi 2 [ 29 ] based systems can accord with the demands of refractoriness, but unfortunately, the zT values of these candidates are far inferior to those of state‐of‐the‐art TE materials (Figure 1c).…”

“…Here, we revisit β-FeSi 2 , which has been long known for its material refractoriness and eco-friendliness (e.g., the natural abundance, low cost of raw materials, and non-toxicity of iron and silicon), yet low zT values. As an indirect bandgap semiconductor with a bandgap value near 0.7 eV, [31] the pristine β-FeSi 2 exhibits a very low zT value of 2 × 10 −4 at 1000 K. [29] Doping Co, [32,33] Mn, [34] or Al [29,35] increases the carrier concentration (n) and helps attain a maximum zT value up to 0.26 at high temperatures. [32] In this paper, we report a doubled zT of 0.62 at 1000 K in refractory β-FeSi 2 by doping iridium (Ir) with a high content (Figure 1c).…”

Enhancing the thermoelectric performance of Sb2Si2Te6 by germanium doping

“…Too high or too low carrier concentration is undesirable for the performance of thermoelectric materials. 1,5,6 For example, for GeTe, the high concentration of Ge vacancies will lead to a high carrier concentration, resulting in a low Seebeck coefficient and high thermal conductivity. [7][8][9][10] Therefore, for state-of-the-art thermoelectric materials, such as Bi 2 Te 3 , CoSb 3 , GeTe, PbTe, SnTe and Mg 3 Sb 2 , it is crucial to optimize the carrier concentration to enhance the PF and zT.…”