Xiaoying Qin

PbTe is recognized as one of the best intermediate-temperature thermoelectric materials; however, its commercial applications are largely restricted by the comparatively lower performance of its n-type counterpart. Here we show that Peierls-Nabarro stress is manipulated through solute-induced lattice softening, which generates high density helical dislocations, dislocation loops, and subgrain boundaries to block heat transport phonons. Concurrently, in-situ formation of Sb ₆ O ₁₃ nanoinclusions resulting from a displacement reaction between Sb and TeO ₂ further suppresses thermal transport, leading to an ultra-low lattice thermal conductivity ( κ _L ≈ 0.21 W m ⁻¹ K ⁻¹ at 773 K). Moreover, Sb doping can simultaneously enhance electronic density of states, leading to the improvement of power factor (16 μW cm ⁻¹ K ⁻² at 563 K). As a result, a remarkably high figure of merit ( ZT ≈ 2.2) is obtained at 723 K in n-type PbTe-1.5 wt%TeO ₂ -1.8 wt%Sb sample. Our findings provide an effective approach to synergistically improve the thermal and electrical properties in advanced thermoelectric materials.

N‐type Bi₂Te_2.7Se_0.3(BTS) is a state‐of‐the‐art thermoelectric material owing to its excellent thermoelectric properties near room temperatures for commercial applications. However, its performance is restricted by its comparatively low figure of merit ZT. Here, it is shown that a 14% increase in power factor (PF) (at 300 K) can be reached through incorporation of inorganic GaAs nanoparticles due to enhanced thermopower originating from the energy‐dependent carrier scattering. Besides, further incorporation of organic nanophase PEDOT: PSS can reduce its lattice thermal conductivity by 59% due to the strong scattering of middle‐ and low‐frequency phonons. As a result, a peak ZT value of ZT_max ≈ 1.31 (at 373 K) and an average ZT_ave ≈ 1.10 (300–473 K) are achieved for the BTS/(0.4 wt.% GaAs + 0.5 wt.% PEDOT: PSS) sample. The present work demonstrates that incorporation of organic–inorganic nanophase is an effective way to improve the performance of BTS.

Bi₂Te₃-based thermoelectric (TE) materials are the state-of-the-art compounds for commercial applications near room temperature. Nevertheless, the application of the n-type Bi₂Te_2.7Se_0.3 (BTS) is restricted by the comparatively low figure of merit (ZT) and intrinsic embrittlement. Here, we show that through dispersion of amorphous Si₃N₄ (a-Si₃N₄) nanoparticles both 14% increase in power factor (at 300 K) and 48% decrease in lattice thermal conductivity are simultaneously realized. The increased power factor comes from enhanced thermopower and reduced electrical resistivity while the reduced lattice thermal conductivity originates mainly from scattering of middle- and low-frequency phonons at the incorporated a-Si₃N₄ nanoparticles. As a result, a large ZT_max = 1.19 (at 373 K) and an average ZT_ave ∼ 1.12 (300–473 K) with better mechanical properties are achieved for the BTS/0.25 wt % Si₃N₄ sample. Present results demonstrate that the incorporation of a-Si₃N₄ is a promising way to improve TE performance.

N-type Bi₂Te_2.7Se_0.3 (BTS) alloy has relatively low thermoelectric performance as compared to its p-type counterpart, which restricts its widespread applications. Herein, we designed and prepared a novel composite system, which consists of an n-type BTS matrix incorporated with both inorganic and organic nanoinclusions. The results indicate that the thermopower of the composite samples can be enhanced by more than 19% upon incorporating inorganic nanophase AgBi₃S₅ (ABS) due to the energy-dependent carrier scattering, which ensures a high power factor. On the other hand, further incorporation of organic nanophase polypyrrole (PPy) can drastically reduce its lattice thermal conductivity owing to the strong scattering of mid- and low-frequency phonons at these nanoinclusions. As a result, high figures of merit ZT_max = 1.3 at 348 K and ZT_ave = 1.17 (300-500 K) are achieved with improved mechanical properties in BTS-based composites incorporated with 1.5 wt % ABS and 0.5 wt % PPy, demonstrating that the incorporation of both inorganic and organic nanoinclusions is an effective way to improve its thermoelectric performance.

Transition-metal dichalcogenide WSe₂ has attracted increasing interest due to its large thermopower (S), low-cost, and environment-friendly constituents. However, its thermoelectric figure of merit, ZT, of WSe₂ is limited due to its large lattice thermal conductivity (κ_L) and low electrical conductivity. In view of WSe₂ and MoS₂ having the same crystal structure, here we designed and prepared Nb-doped quarternary mixed crystal (MC) Nb_0.05W_0.95-xMo_x(Se_1-xS_x)₂ (0 ≤ x ≤ 0.095). The results indicate that the κ_L of the MC can reach as low as 0.12 W m K^-1 at 850 K, being 93% smaller than that of WSe₂. Our analysis reveals that its low κ_L originates chiefly from intense scattering of both high-frequency phonons from point defects (mainly alloying elements) and mid/low-frequency phonons from MoS₂ inclusions residual within MC. In addition, the alloying of WSe₂ with MoS₂ causes a 5-fold increase in cation vacancies (V_W^‴'), leading to a large increase in hole concentration and electrical conductivity, which gives rise to a ∼7.5 times increase in power factor (reaching 4.2 μ W cm^-1 K^-2 at 850 K). As a result, a record high ZT_max = 0.63 is achieved at 850 K for the MC sample with x = 0.076, which is 20 times larger than that of WSe₂, demonstrating that MC Nb_0.05W_0.95-xMo_x(Se_1-xS_x)₂ is a promising thermoelectric material.

Bi₂Te₃-based alloys are the best thermoelectric materials near room temperature.

N-Type Bi₂Te_2.7Se_0.3 (BTS) is the state-of-the-art thermoelectric material near room temperature. However, the figure of merit ZT of commercial BTS ingots is still limited and further improvement is imperative for their wide applications. Here, the results show that through dispersion of the Ag₂Te nanophase in BTS, one can not only elevate its power factor (PF) by as high as 14% (at 300 K) but also reduce its thermal conductivity κ_tot to as small as ∼29% (at 300 K). Experimental evidences show that the improved PF comes from both increased electron mobility via inhibited Te vacancies and enhanced thermopower due to energy filtering effect, while the reduction of κ_tot originates from the drop of both electronic thermal conductivity largely owing to the reduced number of vacancy V_Te^·· and intensified phonon scattering chiefly from the dispersed Ag₂Te nanophase. Consequently, the largest ZT_max = 1.31 (at 350 K) and average ZT_ave = 1.16 (300-500 K) are achieved for the Bi₂Te_2.7Se_0.3-0.3 wt % Ag₂Te composite sample, leading to a projected conversion efficiency η = 8.3% (300-500 K). The present results demonstrate that incorporation of nanophase Ag₂Te is an effective approach to boosting the thermoelectric performance of BTS.

Transition-metal dichalcogenide WSe₂ is a potentially good thermoelectric (TE) material due to its high thermopower (S). However, the low electrical conductivity (σ), power factor (PF), and relatively large lattice thermal conductivity (κ_L) of pristine WSe₂ degenerate its TE performance. Here, we show that through proper substitution of Nb for W in WSe₂, its PF can be increased by ∼10 times, reaching 5.44 μW cm^-1 K^-2 (at 850 K); simultaneously, κ_L lowers from 1.70 to 0.80 W m^-1 K^-1. Experiments reveal that the increase of PF originates from both increased hole concentration due to the replacement of W⁴⁺ by Nb³⁺ and elevated thermopower (S) caused by the enhanced density of states effective mass, while the reduced κ_L comes mainly from phonon scattering at point defects Nb_W. As a result, a record high figure of merit max ∼0.42 is achieved at 850 K for the doped sample W_0.95Nb_0.05Se₂, which is ∼13 times larger than that of pristine WSe₂, demonstrating that Nb doping at the W site is an effective approach to improve the TE performance of WSe₂.