High Thermoelectric Performance in Phonon‐Glass Electron‐Crystal Like AgSbTe₂

Abstract

Achieving glass‐like ultra‐low thermal conductivity in crystalline solids with high electrical conductivity, a crucial requirement for high‐performance thermoelectrics , continues to be a formidable challenge. A careful balance between electrical and thermal transport is essential for optimizing the thermoelectric performance. Despite this inherent trade‐off, the experimental realization of an ideal thermoelectric material with a phonon‐glass electron‐crystal (PGEC) nature has rarely been achieved. Here, PGEC‐like AgSbTe2 is demonstrated by tuning the atomic disorder upon Yb doping, which results in an outstanding thermoelectric performance with figure of merit, zT ≈ 2.4 at 573 K. Yb‐doping‐induced enhanced atomic ordering decreases the overlap between the hole and phonon mean free paths and consequently leads to a PGEC‐like transport behavior in AgSbTe2. A twofold increase in electrical mobility is observed while keeping the position of the Fermi level (EF) nearly unchanged and corroborates the enhanced crystalline nature of the AgSbTe2 lattice upon Yb doping for electrical transport. The cation‐ordered domains, lead to the formation of nanoscale superstructures (≈2 to 4 nm) that strongly scatter heat‐carrying phonons, resulting in a temperature‐independent glass‐like thermal conductivity. The strategy paves the way for realizing high thermoelectric performance in various disordered crystals by making them amorphous to phonons while favoring crystal‐like electrical transport.

Optimizing Thermoelectric Properties through Compositional Engineering in Ag-Deficient AgSbTe2 Synthesized by Arc Melting

“…Disordered, al-scale hierarchical morphology has previously shown lattice contribution below the amorphous limit in SnTe, reaching almost negligible values. , In AgSbTe 2 , this limit is closer to 0.2 W m –1 K –1 that our sample slightly crosses at higher temperatures (Supporting Information, section SI6). Taking into account the enhanced power factor and similar thermal conductivity, the figure of merit ( zT ) calculated for the three samples is higher for Ag 0.7 Sb 1.12 Te 2 and Ag 0.7 Sb 1.12 Te 1.95 Se 0.05 . In the case of Ag 0.7 Sb 1.12 Te 2, a maximum zT of 1.25 at 750 K was determined, while Ag 0.7 Sb 1.12 Te 1.95 Se 0.05 exhibited a maximum of zT of 1.01 at the same temperature (Figure ).…”

“…Chalcogenide materials dominate the field in the mid-temperature range, based on anharmonic bonding in SnSe, band convergence in PbTe, and defect and disorder engineering in AgSbTe 2 derivatives. − The outstanding performance of AgSbTe 2 derivatives is also apparent in well-known (GeTe) m (AgSbTe 2 ) TAGS and (PbTe) m (AgSbTe 2 ) LAST derivatives. − Nevertheless, in recent years, several articles asserted the high conversion efficiency of AgSbTe 2 alone. It displays extremely low thermal conductivity, high values of Seebeck coefficient, and a high figure of merit at fairly low temperatures (500–800 K), filling the vacant range left by SnSe and PbTe. − For instance, Cao et al obtained a peak zT of 1.15 at 623 K, while Wu et al described a peak zT of 1.2 at 500 K in Ag 0.9 Sb 1.1 Te 2 , and the Biswas group reported a zT as high as 2.4 at 573 K in Yb-doped AgSbTe 2 . However, there are several inconsistencies concerning its electrical conductivity, affected by crystalline disorder and different nanoprecipitates, mainly Ag 2 Te, which strongly alter the transport properties.…”

“… 14 − 16 For instance, Cao et al ( 17 ) obtained a peak zT of 1.15 at 623 K, while Wu et al ( 18 ) described a peak zT of 1.2 at 500 K in Ag 0.9 Sb 1.1 Te 2 , and the Biswas group reported a zT as high as 2.4 at 573 K in Yb-doped AgSbTe 2 . 19 However, there are several inconsistencies concerning its electrical conductivity, affected by crystalline disorder and different nanoprecipitates, mainly Ag 2 Te, which strongly alter the transport properties. Roychowdhury et al ( 20 ) described outstanding values of average and peak performance, with zT ≈ 2.6 at 573 K, by employing atomic ordering and a systematic approach to improve carrier mobility in this system through Cd doping, which have been then reproduced using Hg as dopant.…”

Understanding the origin of the high thermoelectric figure of merit of Zintl-phase KCaBi

“…Improvement of ZT requires independent and simultaneous enhancement of the power factor (PF = S 2 s) and reduction of the thermal conductivity (k e + k l ), which is challenging due to the inverse and direct coupled interdependency of S, s, and k e . Large PF and optimized values of S and s can be obtained simultaneously due to the presence of converged dispersed and non-dispersed bands at the band edges of the electronic band structure, 1,2 high and steep density of states in the vicinity of the Fermi level, [3][4][5][6] etc., which may be present by default in some materials [7][8][9][10] due to their unusual structural properties or can be achieved by doping/substituting heavy elements, [11][12][13][14][15][16][17][18] nanostructuring, 19,20 application of pressure, 21 electric field, 22 and lattice strain, [23][24][25][26] and so on. Zintl-phase compounds have been extensively studied in recent years to demonstrate their applicability as thermoelectric materials with high thermoelectric performance caused by a high power factor and very low lattice thermal conductivity.…”

“…Large PF and optimized values of S and σ can be obtained simultaneously due to the presence of converged dispersed and non-dispersed bands at the band edges of the electronic band structure, 1,2 high and steep density of states in the vicinity of the Fermi level, 3–6 etc. , which may be present by default in some materials 7–10 due to their unusual structural properties or can be achieved by doping/substituting heavy elements, 11–18 nanostructuring, 19,20 application of pressure, 21 electric field, 22 and lattice strain, 23–26 and so on.…”