AbstractDue to their amorphous‐like ultralow lattice thermal conductivity both below and above the superionic phase transition, crystalline Cu‐ and Ag‐based superionic argyrodites have garnered widespread attention as promising thermoelectric materials. However, despite their intriguing properties, quantifying their lattice thermal conductivities and a comprehensive understanding of the microscopic dynamics that drive these extraordinary properties are still lacking. Here, an integrated experimental and theoretical approach is adopted to reveal the presence of Cu‐dominated low‐energy optical phonons in the Cu‐based argyrodite Cu7PS6. These phonons yield strong acoustic‐optical phonon scattering through avoided crossing, enabling ultralow lattice thermal conductivity. The Unified Theory of thermal transport is employed to analyze heat conduction and successfully reproduce the experimental amorphous‐like ultralow lattice thermal conductivities, ranging from 0.43 to 0.58 W m−1 K−1, in the temperature range of 100–400 K. The study reveals that the amorphous‐like ultralow thermal conductivity of Cu7PS6 stems from a significantly dominant wave‐like conduction mechanism. Moreover, the simulations elucidate the wave‐like thermal transport mainly results from the contribution of Cu‐associated low‐energy overlapping optical phonons. This study highlights the crucial role of low‐energy and overlapping optical modes in facilitating amorphous‐like ultralow thermal transport, providing a thorough understanding of the underlying complex dynamics of argyrodites.

The structure–property link is inherent to materials. Hexagonal Ge 4 Se 3 Te phase, with special Ge–Ge cationic bonding and distinctive from other IV–VI compounds, reveals thermoelectric (TE) performance far below the common values for IV–VI compounds. Here, it is shown that its TE performance can be substantially enhanced by phase modulation: increasing sintering temperature from 573 to 773 K leads to the decomposition of hexagonal phase into a composite of orthorhombic and rhombohedral phases, which significantly improves TE performance at T ≤ 550 K; Sb/Cd doping stabilizes the rhombohedral phase, compensates the hole concentration, and strengthens the phonon scattering, which further enhances the TE performance over the whole temperature range. The theoretical calculation reveals that the rhombohedral phase has a more favorable electronic band structure than the hexagonal phase for achieving higher electrical transport properties. The optimized TE performance is obtained in rhombohedral Ge 0.90 Sb 0.08 Cd 0.02 Se 0.75 Te 0.25 , with a zT max of 1.36 at 778 K and zT ave of 0.73 from 322 to 778 K, which are among the highest values in the Se‐rich side of Ge(Se, Te) system, and one order higher than those in the hexagonal phase. The study sheds light on the validity of phase modulation for TE performance optimization in Ge(Se, Te)‐based material systems.

Na2S and Si alloying synergistically optimizes the electrical and thermal transport properties of melt-spun p-type Mg2Sn, contributing to a peak thermoelectric zT of 0.52 at 723 K.

Cu3SbSe3 is a promising thermoelectric material with ultralow lattice thermal conductivity, especially at temperatures above 450 K at which the order-disorder transition of copper ions takes place. To investigate whether the high-temperature disordered phase can be extended to lower temperature, a series of Ag-alloyed Cu3-xAgxSbSe3 (x = 0, 0.1, 0.2 and 0.3) polycrystalline samples were synthesized and characterized in this work. It was found that the Ag-alloying shifts the order-disorder transition temperature to lower ones, which is beneficial to the thermoelectric application of Cu3SbSe3. For thermal transport, Ag-alloying is effective in suppressing lattice thermal conductivity in the copper-ions-ordered region, while in the copper-ions-disordered region, Ag-alloying barely has any effect on lattice thermal conductivity, as the phonon scattering is dominated by the liquid-like behavior of copper ions. Although Ag and Cu atoms have the same valence electron number, the carrier concentration is slightly increased after Ag-alloying, which suppresses the bipolar effect and increases the Seebeck coefficient at high temperatures. Finally, a maximum zT of 0.34 is obtained at 652 K for the sample Cu2.7Ag0.3SbSe3, which is 161% higher than that of the pristine sample. (c) 2022 Elsevier B.V. All rights reserved.

We report the influence of Ni substituting for Fe on the phase stability and thermoelectric properties of YbxFe4-yNiySb(12) (x = 0.6, 0.7, 0.8, 0.9, 1.0; y = 1.0, 0.8, 0.6). Ni substituting can efficiently enhance phase stability but reduces band gap, which establishes an optimum Ni substituting content to keep the balance. Meanwhile, the atomic disorder caused by Ni substituting together with Yb-filling leads to a significant reduction in lattice thermal conductivity. The most marked reduction in lattice thermal conductivity is achieved in the Yb0.9Fe3.4Ni0.6Sb12 compound with a minimum value of 0.71 W m(-1) K-1 at about 650 K. Finally, a peak zT of 0.85 is attained at 673 K in the Yb(0.9)Fe(3.4)Ni(0.6)Sb(12)2 compound, which is comparable to other p-type skutterudites at the same temperature. This work highlights the importance of considering the competition between phase stability and band gap when designing high thermoelectric performance co-balt-free skutterudites.(C) 2022 Elsevier B.V. All rights reserved.

In this work, we show significantly enhanced thermoelectric performance in Cu2SnSe3 via a synergistic effect of Cd-doping and CuGaTe2 alloying in the temperature range of 300–823 K. Both the electron and phonon transport properties can be simultaneously regulated by Cd doping at Sn site, leading to a higher quality factor. Meanwhile, a maximum figure of merit (zT) value of ~ 0.68 was obtained for Cu2Sn0.93Cd0.07Se3 sample at 823 K, which is about four times higher than that of the pristine sample (zT = 0.18 at 773 K). Furthermore, Cu2Sn0.93Cd0.07Se3 was alloyed with CuGaTe2 to reduce the lattice thermal conductivity in the high-temperature region. Consequently, a further enhanced zT value (0.77, 823 K) was achieved in the (Cu2Sn0.93Cd0.07Se3)0.94(CuGaTe2)0.06 sample, with a high average zT (zTave) value of 0.30 between 300 and 823 K. These results demonstrate that Cd-doping combined with CuGaTe2 alloying could be an effective method to enhance zT values of Cu2SnSe3 based compounds.

Zintl phase compounds with a CaAl2Si2 structure are promising thermoelectric materials. In this paper, enhanced thermoelectric performance was achieved in SmMg2Bi2, a new member of AB2X2 compounds, via Ca-alloying and Ge-doping. The introduction of point defects by alloying Ca on the Sm site significantly reduces the lattice thermal conductivity, and the lowest value was achieved when the Sm/Ca molar ratio is 1:1. Doping Ge on the Bi site increases the hole concentration of the material, which successfully suppresses the bipolar effect and significantly improves the power factor (PF) in the whole temperature range. Due to the decrease of thermal conductivity and the increase of PF over 323-873 K, the peak zT value of Sm0.5Ca0.5Mg2.15Bi1.99Ge0.01 reached 0.71 at 873 K and the zTave approached 0.44, about 51 and 47% enhancement compared with the pristine sample, respectively. This work provides a thermoelectric performance optimization strategy that can be used for other AB2X2 compounds.

Thermoelectric materials are typically highly degenerate semiconductors, which require high carrier concentration. However, the efficiency of conventional doping by replacing host atoms with alien ones is restricted by solubility limit, and, more unfavorably, such a doping method is likely to cause strong charge‐carrier scattering at ambient temperature, leading to deteriorated electrical performance. Here, an unconventional doping strategy is proposed, where a small trace of alien atoms is used to stabilize cation vacancies in Cu3SbSe4 by compositing with CuAlSe2, in which the cation vacancies rather than the alien atoms provide a high density of holes. Consequently, the hole concentration enlarges by six times but the carrier mobility is well maintained. As a result, a record‐high average power factor of 19 µW cm−1 K−2 in the temperature range of 300–723 K is attained. Finally, with further reduced lattice thermal conductivity, a peak zT value of 1.4 and a record‐high average zT value of 0.72 are achieved within the diamond‐like compounds. This new doping strategy not only can be applied for boosting the average power factor for thermoelectrics, but more generally can be used to maintain carrier mobility for a variety of semiconductors that need high carrier concentration.

SnTe has attracted worldwide attention as a non-toxic candidate material for thermoelectric applications; however, un-modified SnTe possesses inferior thermoelectric properties. Herein, we report the significantly improved thermoelectric performance in Sb, Mn-codoped SnTe synthesized by energy-efficient melt spinning. Sb segregation was observed at the grain boundaries of Sb-doped and Sb, Mn-codoped SnTe melt-spun ribbons, leading to grain refinement; subsequent sintering promotes the diffusion of Sb while retains Sb-rich particles. Initially, intensified phonon scattering from unique multiscale microstructures, including point defects, Sb-rich particles and high-density dislocations generated after Sb doping, effectively diminishes the lattice thermal conductivity of SnTe, leading to a substantially low value of 0.55 W m-1 K-1 in Sn0.84Sb0.16Te at 300 K. Further, the power factors are significantly enhanced via Mn doping owing to valence band convergence, verified by firstprinciples calculation. Consequently, a peak zT of - 1.27 at 773 K and an exceptional average zT of - 0.89 over 300-873 K are obtained in Sn0.72Sb0.16Mn0.12Te, which are - 110% and - 340% higher than those of SnTe, respectively. This study provides an effective pathway to synergistically improve the thermoelectric performance of SnTe by microstructure and band structure engineering, and establishes melt spinning as a controllable synthetic method to high-performance thermoelectrics.

Cu2SnSe3based compounds with a diamond-like structure are promising thermoelectric materials.