Ultrahigh Average Thermoelectric Figure of Merit, Low Lattice Thermal Conductivity and Enhanced Microhardness in Nanostructured (GeTe)_x(AgSbSe₂)_100−x

Abstract

Waste heat sources are generally diffused and provide a range of temperatures rather than a particular temperature. Thus, thermoelectric waste heat to electricity conversion requires a high average thermoelectric figure of merit (ZT ) of materials over the entire working temperature along with a high peak thermoelectric figure of merit (ZT ). Herein an ultrahigh ZT of 1.4 for (GeTe) (AgSbSe ) [TAGSSe-80, T=tellurium, A=antimony, G=germanium, S=silver, Se=selenium] is reported in the temperature range of 300-700 K, which is one of the highest values measured amongst the state-of-the-art Pb-free polycrystalline thermoelectric materials. Moreover, TAGSSe-80 exhibits a high ZT of 1.9 at 660 K, which is reversible and reproducible with respect to several heating-cooling cycles. The high thermoelectric performance of TAGSSe-x is attributed to extremely low lattice thermal conductivity (κ ), which mainly arises due to extensive phonon scattering by hierarchical nano/meso-structures in the TAGSSe-x matrix. Addition of AgSbSe in GeTe results in κ of ≈0.4 W mK in the 300-700 K range, approaching to the theoretical minimum limit of lattice thermal conductivity (κ ) of GeTe. Additionally, (GeTe) (AgSbSe ) exhibits a higher Vickers microhardness (mechanical stability) value of ≈209 kgf mm compared to the other state-of-the-art metal chalcogenides, making it an important material for thermoelectrics.

Employing Interfaces with Metavalently Bonded Materials for Phonon Scattering and Control of the Thermal Conductivity in TAGS‐x Thermoelectric Materials

“…The intrinsic lattice thermal conductivity of AgSbTe 2 and GeTe is about 0.7 and 2.6 W mK −1 , respectively. [ 33,34 ] Intuitively, it might be normal to expect a lower lattice thermal conductivity with increasing the content of AgSbTe 2 in the TAGS system. However, the κ l value at room temperature for TAGS‐75, TAGS‐80, and TAGS‐85 was reported to be 0.8, 0.6, and 0.7 W mK −1 , respectively.…”

“…Similar to AgSbTe 2 , AgSbSe 2 has also an intrinsically low lattice thermal conductivity due to the large anharmonicity. Samanta et al [ 34 ] reported that the lattice thermal conductivity is minimized in the compound with 20 at% AgSbSe 2 . Adding more AgSbSe 2 oppositely increases the lattice thermal conductivity.…”

High‐Performance GeTe‐Based Thermoelectrics: from Materials to Devices

“…Histogram of Vickers microhardness, H v values of GeTe‐based thermoelectric materials and typical metal chalcogenides. [ 77,96,153–157 ] …”

“…[ 77 ] Moreover, H v value of (GeTe) 80 (AgSbSe 2 ) 20 is effectively improved to 209 Kgf mm −2 through suppressing the expansion of nano‐ and microcracks with AgSbSe 2 nanoprecipitates. [ 153 ] Comparing with other high‐performance chalcogenide thermoelectric materials, GeTe exhibits relatively higher H v values, indicating a better mechanical stability.…”

High Thermoelectric Performance of New Rhombohedral Phase of GeSe stabilized through Alloying with AgSbSe2

“…[30,37,38] Forr hombohedral GeSe,t he band structure is quite similar to that of rhombohedral GeTe, ag ood thermoelectric material (TAGS). [25][26][27][28][29] Rhombohedral GeTee xhibits high carrier concentration due to intrinsic Ge vacancies. [39][40][41] Theformation energy of Ge vacancies in rhombohedral GeTe is low meaning Ge vacancies can form easily.…”