High Thermoelectric Performance of AgSb_1–xPb_xSe₂ Prepared by Fast Nonequilibrium Synthesis

Abstract

AgSbSe 2 is a typical member of cubic I−V−VI 2 semiconductors, which are known for their extremely low lattice thermal conductivity (κ l ). However, the low electrical conductivity of AgSbSe 2 , below ∼10 S cm −1 at room temperature, has hindered its thermoelectric performance. In this work, single-phase AgSbSe 2 bulk samples with much higher electrical conductivity were synthesized via self-propagating hightemperature synthesis (SHS) combined with spark plasma sintering (SPS) for the first time. Pb doping through the nonequilibrium process further increases the electrical conductivity to >100 S cm −1 . Furthermore, continuously increased effective mass m d * can be achieved upon Pb doping because of the multiple degenerate valence bands of AgSbSe 2 and the energy-filtering effect induced by in situ-formed nanodots. The simultaneous enhancement of both the electrical conductivity and Seebeck coefficient contributes to an unprecedentedly high average power factor of 6.75 μW cm −1 K −2 . Meanwhile, the introduced dense grain boundaries and point defects enhance the phonon scattering and consequently suppress κ l , yielding a high ZT value of 1.2 at 723 K in AgSb 0.94 Pb 0.06 Se 2 . This study opens a new avenue for rapid, low-cost, large-scale production of AgSbSe 2 -based materials and demonstrates that Pb-doped AgSbSe 2 prepared via the SHS−SPS method is a promising candidate for thermoelectric applications.

Advances and Challenges of AgSbSe2‐based Thermoelectric Materials

“…Recently, it is revealed that synthesis condition also plays a role in tuning the carrier concentration of AgSbSe 2 [41,60,73,75] . Gao et al [73] .…”

“…At room temperature, cations disordering model seems to better describe the Xray diffraction (XRD) results of AgSbSe 2 than ordering rhombohedral structure does. [41,48,49] However, it is worth noting that powder XRD patterns with CuKα radiation may not be able to distinguish whether cations are ordered or not in AgSbSe 2 because of the very similar X-ray scattering factors of Ag and Sb. [45] At this point, neutron diffraction might be a better tool to probe the possible cation ordering in AgSbSe 2 because of its higher resolution and accuracy.…”

“…Recently, it is revealed that synthesis condition also plays a role in tuning the carrier concentration of AgSbSe 2 . [41,60,73,75] Gao et al [73] found that the ball-milled nanostructuring AgSbSe 2 has higher carrier concentration (1.6 × 10 19 cm À 3 ) than its coarsegrained ingots (0.6 × 10 19 cm À 3 ) at room temperature. As a strong plastic deformation process, ball-milling usually induces rich defects in samples and induces changes of carrier density.…”

“…[41] The added interfaces of the in situ-formed nanodots effectively filter out low-energy charge carriers that have a negative contribution to the Seebeck coefficient. This is [34,41,44,52,62,65,73,74] (b) RT power factor as a function of carrier concentration from available literatures. [34,41,44,48,52,62,65,74] known as energy-filtering effect (schematically displayed in Figure 5b), namely, carriers are selectively transmitted through the host-guest interfaces.…”

“…For instance, through careful carrier concentration regulation and rational composition design, a peak ZT of 1.2 has been achieved in 6 mol% Pb-doped AgSbSe 2 . [41] This mini-review provides a timely update on recent advances of AgSbSe 2 in thermoelectric research, with a focus on the relationship between structural properties and thermoelectric performance. We first discuss about the debate on whether or not Ag/Sb atoms are orderly arranged within the cationic sites and its influence on the electronic band structure of AgSbSe 2 .…”