It is common sense that a phase interface (or grain boundary) could be used to scatter phonons in thermoelectric (TE) materials, resulting in low thermal conductivity (κ). However, a large number of impurity phases are always so harmful to the transport of carriers that poor TE performance is obtained. Here, we demonstrate that numerous superior multiphase (AgCuTe, Ag₂Te, copper telluride (Cu₂Te and Cu_2−xTe), and nickel telluride (NiTe)) interfaces with simultaneous strong phonon scattering and weak electron scattering could be realized in AgCuTe-based TE materials. Owing to the similar chemical bonds in these phases, the depletion region at phase interfaces, which acts as carrier scattering centers, could be ignored. Therefore, the power factor (PF) is obviously enhanced from ~609 to ~832 μW·m⁻¹·K⁻², and κ is simultaneously decreased from ~0.52 to ~0.43 W·m⁻¹·K⁻¹ at 636 K. Finally, a peak figure of merit (zT) of ~1.23 at 636 K and an average zT (zT_avg) of ~1.12 in the temperature range of 523–623 K are achieved, which are one of the best values among the AgCuTe-based TE materials. This study could provide new guidance to enhance the performance by designing superior multiphase interfaces in the TE materials.

The argyrodite compounds ( ${\text{A}}_{(12-n)/m}^{m+}{\text{B}}^n{}^{+}{\text{X}}_6^{2-}$(A^m+ = Li⁺, Cu⁺, and Ag⁺; Bⁿ⁺ = Ga³⁺, Si⁴⁺, Ge⁴⁺, Sn⁴⁺, P⁵⁺, and As⁵⁺; and X^2-= S^2-, Se^2-, or Te^2-)) have attracted great attention as excellent thermoelectric (TE) materials due to their extremely low lattice thermal conductivity (κ_l). Among them, Ag₈SnSe₆-based TE materials have high potential for TE applications. However, the pristine Ag₈SnSe₆ materials have low carrier concentration (< 10¹⁷ cm^-3), resulting in low power factors. In this study, a hydrothermal method was used to synthesize Ag₈SnSe₆ with high purity, and the introduction of SnBr₂ into the pristine Ag₈SnSe₆ powders has been used to simultaneously increase the power factor and decrease the thermal conductivity (κ). On the one hand, a portion of the Br^- ions acted as electrons to increase the carrier concentration, increasing the power factor to a value of ~698 μW·m^-1·K^-2 at 736 K. On the other hand, some of the dislocations and nanoprecipitates (SnBr₂) were generated, resulting in a decrease of κ_l (~0.13 W·m^-1·K^-1) at 578 K. As a result, the zT value reaches ~1.42 at 735 K for the sample Ag₈Sn_1.03Se_5.94Br_0.06, nearly 30% enhancement in contrast with that of the pristine sample (~1.09). The strategy of synergistic manipulation of carrier concentration and microstructure by introducing halogen compounds could be applied to the argyrodite compounds to improve the TE properties.

Eco-friendly SnTe based thermoelectric materials are intensively studied recently as candidates to replace PbTe; yet the thermoelectric performance of SnTe is suppressed by its intrinsically high carrier concentration and high thermal conductivity. In this work, we confirm that the Ag and La co-doping can be applied to simultaneously enhance the power factor and reduce the thermal conductivity, contributing to a final promotion of figure of merit. On one hand, the carrier concentration and band offset between valence bands are concurrently reduced, promoting the power factor to a highest value of ~2436 μW·m^-1·K^-2 at 873 K. On the other hand, lots of dislocations (~3.16×10⁷ mm^-2) associated with impurity precipitates are generated, resulting in the decline of thermal conductivity to a minimum value of 1.87 W·m^-1·K^-1 at 873 K. As a result, a substantial thermoelectric performance enhancement up to zT ≈ 1.0 at 873 K is obtained for the sample Sn_0.94Ag_0.09La_0.05Te, which is twice that of the pristine SnTe (zT ≈ 0.49 at 873 K). This strategy of synergistic manipulation of electronic band and microstructures via introducing rare earth elements could be applied to other systems to improve thermoelectric performance.