Low Sound Velocity Contributing to the High Thermoelectric Performance of Ag₈SnSe₆

Abstract

Conventional strategies for advancing thermoelectrics by minimizing the lattice thermal conductivity focus on phonon scattering for a short mean free path. Here, a design of slow phonon propagation as an effective approach for high‐performance thermoelectrics is shown. Taking Ag8SnSe6 as an example, which shows one of the lowest sound velocities among known thermoelectric semiconductors, the lattice thermal conductivity is found to be as low as 0.2 W m−1 K−1 in the entire temperature range. As a result, a peak thermoelectric figure of merit zT > 1.2 and an average zT as high as ≈0.8 are achieved in Nb‐doped materials, without relying on a high thermoelectric power factor. This work demonstrates not only a guiding principle of low sound velocity for minimal lattice thermal conductivity and therefore high zT, but also argyrodite compounds as promising thermoelectric materials with weak chemical bonds and heavy constituent elements.

High thermoelectric performance and low thermal conductivity in Cu2−yS1/3Se1/3Te1/3 liquid-like materials with nanoscale mosaic structures

“…The temperature dependence of the calculated minimum thermal conductivity κmin for Cu2S1/3Se1/3Te1/3 is shown in Figure 7c (red dashed line). Interestingly, the calculated κmin value (~0.49 W m -1 K -1 ) is higher than the measured lattice thermal conductivity over the whole temperature range, which is in accordance with observations made on the other liquid-like compounds Cu2Se, Ag8SnSe6, and Cu7PSe6 [10,38,39]. The abnormal low lattice thermal conductivity in these superionic conductors can be attributed to their special 'PLEC' character.…”

Achieving zT > 2 in p‐Type AgSbTe2−xSex Alloys via Exploring the Extra Light Valence Band and Introducing Dense Stacking Faults

“…[2] Accordingly, the dimensionless figure-of-merit, zT (= S 2 σT/κ), has been defined to quantify thermoelectric performance. [4] To obtain a low κ l , intrinsically, liquid phonons, [5] lattice anharmonicity, [6] and low sound velocity [7] can dampen the proliferation of phonons significantly, and extrinsically, nanoscale mosaicity, [8] nanostructuring, [9] hierarchical architecturing, [4c,10] and matrix with nanoprecipitates [11] are effective to further enhance phonon scatterings. [4] To obtain a low κ l , intrinsically, liquid phonons, [5] lattice anharmonicity, [6] and low sound velocity [7] can dampen the proliferation of phonons significantly, and extrinsically, nanoscale mosaicity, [8] nanostructuring, [9] hierarchical architecturing, [4c,10] and matrix with nanoprecipitates [11] are effective to further enhance phonon scatterings.…”

Electronic origin of the high thermoelectric performance of GeTe among the p-type group IV monotellurides

“…Effective approaches include nanostructuring, 2-7 lattice anharmonicity, 8,9 liquid phonons, 10,11 vacancy [12][13][14] or interstitial 15 point defects and a low sound velocity. 16 Band engineering concepts including a large number of degenerated bands, [17][18][19][20][21][22][23][24][25] a low band effective mass 26 and weak carrier scattering 27 have also proven to be successful in enhancing the TE performance. The knowledge of the band structure is thus critical for band engineering and optimizing the electrical transport of TE materials.…”