Owing to the intrinsically good near-room-temperature thermoelectric performance, β-Ag2Se has been considered as a promising alternative to n-type Bi2Te3 thermoelectric materials. Herein, we develop an energy- and time-efficient wet mechanical alloying and spark plasma sintering method to prepare porous β-Ag2Se with hierarchical structures including high-density pores, a metastable phase, nanosized grains, semi-coherent grain boundaries, high-density dislocations, and localized strains, leading to an ultralow lattice thermal conductivity of ∼0.35 W m–1 K–1 at 300 K. A relatively high carrier mobility is obtained by adjusting the sintering temperature to obtain pores with an average size of ∼260 nm, therefore resulting in a figure of merit, zT, of ∼0.7 at 300 K and ∼0.9 at 390 K. The single parabolic band model predicts that zT of such porous β-Ag2Se can reach ∼1.1 at 300 K if the carrier concentration can be tuned to ∼1 × 1018 cm–3, suggesting that β-Ag2Se can be a competitive candidate for room-temperature thermoelectric applications.
β -Ag 2 Se holds a great promise for wearable thermoelectric generators due to its good mechanical properties and biocompatibility. However, optimizing its power factor through alterations in the Ag/Se stoichiometric ratio or incorporating secondary phases has reached the limitation. This work adopts a liquid-like sintering strategy, namely employing the migration and precipitation of silver ions from metallic silver to the silver selenide during the spark plasma sintering process to construct significantly sized and coherent Ag-rich nanoprecipitates within flexible Ag/ β -Ag 2 Se composite films, thereby achieving an unprecedented power factor exceeding 4000 μWm −1 K −2 at 303 K. The Ag-rich nanoprecipitates play a crucial role in elevating the carrier concentration, enhancing the density-of-states effective mass, and mitigating carrier scattering caused by phase interfaces and acoustic phonons. The generator containing 5 pieces of optimal films shows an normalized output power density of 10.89 μWcm −1 K −2 under a temperature difference of 26.0 K. This study strongly suggests that the creation of Ag-rich nanoprecipitates is an effective avenue for improving the electrical performance of β -Ag 2 Se-based thermoelectric materials.
Jie Chen,Qiang Sun,Deyu Bao,Bang-Zhou Tian,Zegao Wang,Jun Tang,Dali Zhou,Lei Yang,Zhi-Gang Chen
Thermoelectric materials strengthened by defect engineering can also suffer from the compromise of plasticity, and in turn results in negative effect on the processability, reliability and durability of thermoelectric devices. Here, we introduce nano-twinned CuAgSe secondary phase to achieve simultaneously increased compressive strength and plasticity of the β-Ag 2 Se pellets without obviously sacrificing the thermoelectric performance, as evidenced by our thermoelectric measurements. Our pellet shows a maximum compressive strength of 96 MPa, which is ∼104% higher than that of pristine Ag 2 Se, ascribed to the impeded crack propagation by the CuAgSe secondary phase. An extraordinary deformation value of ∼19% is observed at the maximum compressive strength, which is attributed to the intrinsically large plastic deformation of the Ag 2 Se matrix, the deformable nano-twinned CuAgSe secondary as well as the interaction between the Ag 2 Se matrix and the CuAgSe secondary phase. This work indicates that introducing nano-twinned secondary phase in thermoelectric materials is a promising strategy for developing high-performance thermoelectric materials with high strength and plasticity.
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