Three‐Stage Inter‐Orthorhombic Evolution and High Thermoelectric Performance in Ag‐Doped Nanolaminar SnSe Polycrystals

Abstract

generation in deep-space and waste heat recovery from vehicle exhaust, as well as ice-free refrigeration in wine-storage cabinets, hotel room mini-refrigerators, and office water coolers. [1][2][3][4][5] The performance of TE materials is determined by the dimensionless figure of merit (ZT), defined as ZT = α 2 σT/(κ lat + κ ele ), where α, σ, κ lat , κ ele , and T are the Seebeck coefficient, electrical conductivity, lattice thermal conductivity, electronic thermal conductivity, and absolute temperature, respectively. The conversion efficiency for these potential applications requires high ZT over a wide range of temperatures. [6] For effective waste heat recovery in vehicles under a 350 K temperature differential, the average or device ZT (ZT dev ) should be about 1.25 in order to increase mileage up to 10%, [1,7] while for primary power generation, an average ZT of more than 1.5 is required under an 800 K temperature differential. [1,7] Recently, SnSe single crystals have produced a surge in the field of thermoelectrics as a new type of promising TE materials because of the intrinsically ultralow thermal conductivity (<0.4 W m −1 K −1 at 923 K) and high ZT along the b-and c-crystallographic directions (>2.3 at 923 K). [8] A new record of ZT dev ≈ 1.34 from 300-773 K along the b-crystallographic direction was achieved in thermoelectric device fabricated from hole-doped SnSe single crystal. [9] Nevertheless, the difficulties in large-scale synthesis of single crystals limit their practical applications, and extensive efforts have been devoted to the fabrication of high-performance polycrystalline counterparts. [10][11][12][13][14][15] For example, Wei et al. [12] reported a ZT of ≈0.8 at 800 K in 1% Na-and K-doped SnSe, which was produced by conventional solid state reaction followed by a spark plasma sintering (SPS) treatment. Due to an impressively low lattice thermal conductivity (≈0.20 W m −1 K −1 at 773 K) arising from the presence of coherent nanoprecipitates in the SnSe matrix, a high ZT of ≈1.1 at 773 K was achieved in the direction perpendicular to the pressing direction of SPS for ball-milled K-doped SnSe. [11] Apart from p-type alkali dopants (Li, Na, K), n-type dopants such as I and BiCl 3 are also adopted to improve the performance of polycrystalline SnSe. [14,16] For instance, a ZT of ≈0.8 at 773 K was obtained in I-doped SnSe polycrystals, whichThe ultrahigh thermoelectric performance of SnSe-based single crystals has attracted considerable interest in their polycrystalline counterparts. However, the temperature-dependent structural transition in SnSe-based thermoelectric materials and its relationship with their thermoelectric performance are not fully investigated and understood. In this work, nanolaminar SnSe polycrystals are prepared and characterized in situ using neutron and synchrotron powder diffraction measurements at various temperatures. Rietveld refinement results indicate that there is a complete inter-orthorhombic evolution from Pnma to Cmcm by a series of layer slips and stretches a...

High-performance SnSe thermoelectric materials: Progress and future challenge

“…Figure 27(g) is a HRTEM image taken from a sintered SnSe pellet [119], and shows nanosized grains with disordered atomic planes with dislocations (marked by dashed circle) and lattice curvatures (marked by dashed line) [119]. For doping with other elements (such as Na [274] and Ag [268]), Figure 27(h) shows a HRTEM image of Ag-doped SnSe [275], from which a dark area was observed to be predicted to be amorphous. In terms of incorporating with other compounds (such as SnTe), Figure 27(i) shows a TEM image of the boundary of two phases for SnSe and SnTe [276].…”

“…In order to decouple σ, S [275]. From which, a high S 2 of ~4.5 μW cm -1 K -2 and a low κ of ~0.23 W m -1 K -1 were achieved, leading to a high peak ZT of 1.1 at 773 K [275].…”

High Thermoelectric Performance in Polycrystalline SnSe Via Dual‐Doping with Ag/Na and Nanostructuring With Ag8SnSe6

“…The peak ZT of pristine polycrystalline SnSe (≈0.6 at 773 K) [23] is much lower than that of the single crystalline counterparts. [25] So far, several effective strategies have been adopted to enhance the electrical conductivity of polycrystalline SnSe, such as alkali metal (Li, Na, K), [23,26] Ag, [27,28] Cu, [29] and Zn [30] doping at Sn sites and Sn vacancies. [25] So far, several effective strategies have been adopted to enhance the electrical conductivity of polycrystalline SnSe, such as alkali metal (Li, Na, K), [23,26] Ag, [27,28] Cu, [29] and Zn [30] doping at Sn sites and Sn vacancies.…”

“…[25] So far, several effective strategies have been adopted to enhance the electrical conductivity of polycrystalline SnSe, such as alkali metal (Li, Na, K), [23,26] Ag, [27,28] Cu, [29] and Zn [30] doping at Sn sites and Sn vacancies. [28] Despite the relative high ZT value achieved, the average power factor for the Ag 0.015 Sn 0.985 Se is still low (≈5.0 µW cm −1 K −2 from 300 to 973 K). [28] Despite the relative high ZT value achieved, the average power factor for the Ag 0.015 Sn 0.985 Se is still low (≈5.0 µW cm −1 K −2 from 300 to 973 K).…”

Application Prospects of Thermoelectric Technique

“…A uniquely capable source of power is the radioisotope thermoelectric generator (RTG), which direct converts heat from the natural decay of radioisotope materials, often plutonium-238, into electricity. Up to now, series spacecrafts including the Apollo missions (to the Moon, Figure 1b), the Curiosity missions (to the Mars), and Voyager missions (outer Solar System) are all powered by RTGs because of their reliability and universal [2][3][4]. …”