Identifying the Specific Nanostructures Responsible for the High Thermoelectric Performance of (Bi,Sb)₂Te₃ Nanocomposites

Abstract

Herein, we report the synthesis of multiscale nanostructured p-type (Bi,Sb)(2)Te(3) bulk materials by melt-spinning single elements of Bi, Sb, and Te followed by a spark plasma sintering process. The samples that were most optimized with the resulting composition (Bi(0.48)Sb(1.52)Te(3)) and specific nanostructures showed an increase of approximately 50% or more in the figure of merit, ZT, over that of the commercial bulk material between 280 and 475 K, making it suitable for commercial applications related to both power generation and refrigeration. The results of high-resolution electron microscopy and small angle and inelastic neutron scattering along with corresponding thermoelectric property measurements corroborate that the 10-20 nm nanocrystalline domains with coherent boundaries are the key constituent that accounts for the resulting exceptionally low lattice thermal conductivity and significant improvement of ZT.

Microstructure Analysis and Thermoelectric Properties of Melt-Spun Bi-Sb-Te Compounds

“…As shown in Figure 1, increasing wheel rotation speed from 1000 rpm to 4000 rpm results in a decrease of the ribbon thickness from 17.8 μm to 3.38 μm. The thickness is inversely proportional with the wheel rotation speed, which is in good agreement with the previous reports [24,25], and the meltspun ribbon is composed of non-crystalline contact surface and crystalline free surface [20]. The nanostructure of the free surface also changes with the wheel rotation speed, as shown in Figure 2.…”

“…After the MS process, we can obtain thin and short (~2 mm in width and ~10 mm in length) ribbon-shaped materials with an amorphous structure on the contact surface and nano-scale structure on the free surface [20]. The Cu wheel rotation speed during the MS process would be a major factor determining the cooling rate.…”

“…However, these technologies are still far from commercialization in terms of mass production. The continuous attempts to reduce grain size of the TE materials have been tried via high-energy ball milling [15,16], spark erosion [17], melt spinning (MS) [8,[18][19][20], and bottom-up chemical synthesis processes [21][22][23].…”

“…According to several reports [8,[18][19][20], the MS process is proven to be effective for the realization of nano-scale sized Bi 2 Te 3 -based TE materials. However, it is necessary to investigate the process variables, leading to different microstructures and transport properties which are critical factors for TE performance.…”

Thermoelectric Properties of Amorphous Zr-Ni-Sn Thin Films Deposited by Magnetron Sputtering

“…Recently, bulk ternary half-Heusler (HH) compounds such as MNiSn and MCoSb (M = Ti, Zr, and Hf) have exhibited excellent transport properties and ZT values close to those of state-of-the-art materials such as PbTeand Bi 2 Te 3 -based compounds. [3][4][5][6][7][8] For MNiSn-based HH compounds, it has been found that a small amount of Sb doping can enhance ZT, with reliable values of 0.8 to 1.0. 9,10 For MCoSb-based HH compounds, ZT values have been improved to 0.51 owing to a remarkable reduction of the thermal conductivity.…”