Fundamental manipulation of phonon dispersion, and thus phonon transport, relies on a change either in atomic mass (M) or in interaction force between atoms (F). Existing approaches focusing on M usually require a large variation in composition that may risk a reduction in carrier mobility. This work reveals that a manipulation of F by lattice strain through thermodynamically stable in-grain dislocations is particularly effective for minimizing the lattice thermal conductivity (k L ), leading to an extraordinary thermoelectric figure of merit in PbTe.

Achieving higher carrier mobility plays a pivotal role for obtaining potentially high thermoelectric performance. In principle, the carrier mobility is governed by the band structure as well as by the carrier scattering mechanism. Here, we demonstrate that by manipulating the carrier scattering mechanism in n-type MgSb-based materials, a substantial improvement in carrier mobility, and hence the power factor, can be achieved. In this work, Fe, Co, Hf, and Ta are doped on the Mg site of MgSbBiTe, where the ionized impurity scattering crosses over to mixed ionized impurity and acoustic phonon scattering. A significant improvement in Hall mobility from ∼16 to ∼81 cm⋅V⋅s is obtained, thus leading to a notably enhanced power factor of ∼13 μW⋅cm⋅K from ∼5 μW⋅cm⋅K A simultaneous reduction in thermal conductivity is also achieved. Collectively, a figure of merit () of ∼1.7 is obtained at 773 K in MgCoSbBiTe The concept of manipulating the carrier scattering mechanism to improve the mobility should also be applicable to other material systems.

Point defects, which scatter electronic carriers as well as phonons, play a vital role in the transport properties of thermoelectric materials. Therefore, defect engineering can be utilized for tuning thermoelectric properties. Mg vacancies, as the dominant defects in the ntype Mg 3 Sb 2 -based materials, can greatly impact the transport properties of this compound. Here we demonstrate that the Mg vacancies in the n-type Mg 3 Sb 2 -based materials can be successfully manipulated by simply tuning the preparation conditions. A substantial enhancement in the Hall mobility is obtained, from ∼39 to ∼128 cm 2 V −1 s −2 , an increase of ∼228%. The significantly improved Hall mobility noticeably boosts the power factor from ∼6 to ∼20 μW cm −1 K −2 and effectively enhances the thermoelectric figure of merit. Our results demonstrate that defect engineering could be very effective in improving the thermoelectric performance of n-type Mg 3 Sb 2based materials.

Ternary half‐Heusler (HH) alloys display intriguing functionalities ranging from thermoelectric to magnetic and topological properties. For thermoelectric applications, stable HH alloys with a nominal valence electron count (VEC) of 18 per formula or defective HH alloys with a VEC of 17 or 19 are assumed to be promising candidates. Inspired by the pioneering efforts to design a TiFe0.5Ni0.5Sb double HH alloy by combining 17‐electron TiFeSb and 19‐electron TiNiSb HH alloys, both high‐performance n‐type and p‐type materials based on the same parent TiFe0.5Ni0.5Sb are developed. First‐principles calculation results demonstrate their beneficial band structure having a high band degeneracy that contributes to their large effective mass and thereby maintains their high Seebeck coefficient values. Due to the strong Fe/Ni disorder effect, TiFe0.5Ni0.5Sb exhibits a much lower lattice thermal conductivity than does TiCoSb, consistent with very recently reported results. Furthermore, tuning the ratio of Fe and Ni leads to achieving both p‐ and n‐types, and alloying Ti by Hf further enhances the thermoelectric performance significantly. A peak ZT of ≈1 and ≈0.7 at 973 K are achieved in the p‐type and n‐type based on the same parent, respectively, which are beneficial and promising for real applications.

PbTe has been leading the advancements in the field of thermoelectricity due to its capability for demonstrating and integrating various new concepts. However, the toxicity of Pb is always a concern for terrestrial applications, which inspired great advancement to be achieved very recently in its alternative analogue SnTe. Challenges making p-type SnTe as thermoelectrically efficient as PbTe rely on a reduction of its carrier concentration, valence band offset, and lattice thermal conductivity. Utilization of newly developed concepts including both band and defect engineering amazingly increases the thermoelectric figure of merit, zT, from 0.4 up to 1.6 while remaining a nontoxic composition. The corresponding conceptual route diagram is surveyed, and future considerations on composition, crystal structure, and microstructure for further advancements are discussed in this Perspective. Concepts discussed here not only have promoted SnTe as a highly efficient environment-friendly thermoelectric material but also guided advancements in many other thermoelectrics.

a b s t r a c tSnSe as a lead-free IVeVI semiconductor, has attracted intensive attention for its potential thermoelectric applications, since it is less toxic and much cheaper than conventional PbTe and PbSe thermoelectrics. Here we focus on its sister layered compound SnSe 2 in n-type showing a thermoelectric performance to be similarly promising as SnSe in the polycrystalline form. This is enabled by its favorable electronic structure according to first principle calculations, its capability to be effectively doped by bromine on selenium site to optimize the carrier concentration, as well as its intrinsic lattice thermal conductivity as low as 0.4 W/m-K due to the weak van der Waals force between layers. The broad carrier concentration ranging from 0.5 to 6 Â 10 19 cm À3 realized in this work, further leads to a fundamental understanding on the material parameters determining the thermoelectric transport properties, based on a single parabolic band (SPB) model with acoustic scattering. The layered crystal structure leads to a texture in hot-pressed polycrystalline materials and therefore anisotropic transport properties, which can be well understood by the SPB model. This work not only demonstrates SnSe 2 as a promising thermoelectric material but also guides the further improvements particularly by band engineering and texturing approaches.

Aliovalent defects are extremely effective in manipulating charge transport and atomic vibrational properties for thermoelectric enhancements. Electronic performance of thermoelectrics is optimized at a reduced Fermi level of $0.3, which causes the optimal carrier concentration (n opt) to be strongly temperature dependent. This motivates a dynamic doping approach for electronic enhancements through an increase with temperature of solubility of aliovalent dopants. In addition, the defects could simultaneously act as scattering sources of phonons for reducing the lattice thermal conductivity. These effects are illustrated in this work by the temperature-dependent excess Cu solubility in n-PbTe 0.75 Se 0.25 thermoelectrics, in which both carriers and dislocations are induced for regulating the electronic and phononic transport properties for a realization of an extraordinary thermoelectric figure of merit. The resultant defect structures and temperature gradient doping effects (for aliovalent solutes) could in principle open extra possibilities for optimizing charge and phonon transport properties in thermoelectrics.

In‐grain dislocation‐induced lattice strain fluctuations are recently revealed as an effective avenue for minimizing the lattice thermal conductivity. This effect could be integratable with electronic enhancements such as by band convergence, for a great advancement in thermoelectric performance. This motivates the current work to focus on the thermoelectric enhancements of p‐type PbTe alloys, where monotelluride‐alloying and Na‐doping are used for a simultaneous manipulation on both dislocation and band structures. As confirmed by synchrotron X‐ray diffractions and Raman measurements, the resultant dense in‐grain dislocations induce lattice strain fluctuations for broadening the phonon dispersion, leading to an exceptionally low lattice thermal conductivity of ≈0. 4 W m‐K−1. Band structure calculations reveal the convergence of valence bands due to monotelluride‐alloying. Eventually, the integration of both electronic and thermal improvements lead to a realization of an extraordinary figure of merit zT of ≈2.5 in Na0.03Eu0.03Cd0.03Pb0.91Te alloy at 850 K.