SnSe: a remarkable new thermoelectric material

High-efficiency thermoelectric materials require simultaneously high power factors and low thermal conductivities. Aligning band extrema to achieve high band degeneracy, as realized in PbTe, is one of the most efficient approaches to enhance power factor. However, this approach usually relies on band structure engineering, e.g., via chemical doping or strain. By employing first-principles methods with explicit computation of phonon and carrier lifetimes, here we show two full-Heusler compounds Li2TlBi and Li2InBi have exceptionally high power factors and low lattice thermal conductivities at room temperature. The expanded rock-salt sublattice of these compounds shifts the valence band maximum to the middle of the Σ line, increasing the band degeneracy by a factor of three. Meanwhile, resonant bonding in the PbTe-like sublattice and soft Tl–Bi (In–Bi) bonding interaction is responsible for intrinsic low lattice thermal conductivities. Our results present an alternative strategy of designing high performance thermoelectric materials.

Artificial nanostructures have improved prospects of thermoelectric systems by enabling selective scattering of phonons and demonstrating significant thermal conductivity reductions. While the low thermal conductivity provides necessary temperature gradients for thermoelectric conversion, the heat generation is detrimental to electronic systems where high thermal conductivity are preferred. The contrasting needs of thermal conductivity are evident in thermoelectric cooling systems, which call for a fundamental breakthrough. Here we show a silicon nanostructure with vertically etched holes, or holey silicon, uniquely combines the low thermal conductivity in the in-plane direction and the high thermal conductivity in the cross-plane direction, and that the anisotropy is ideal for lateral thermoelectric cooling. The low in-plane thermal conductivity due to substantial phonon boundary scattering in small necks sustains large temperature gradients for lateral Peltier junctions. The high cross-plane thermal conductivity due to persistent long-wavelength phonons effectively dissipates heat from a hot spot to the on-chip cooling system. Our scaling analysis based on spectral phonon properties captures the anisotropic size effects in holey silicon and predicts the thermal conductivity anisotropy ratio up to 20. Our numerical simulations demonstrate the thermoelectric cooling effectiveness of holey silicon is at least 30% greater than that of high-thermal-conductivity bulk silicon and 400% greater than that of low-thermal-conductivity chalcogenides; these results contrast with the conventional perception preferring either high or low thermal conductivity materials. The thermal conductivity anisotropy is even more favorable in laterally confined systems and will provide effective thermal management solutions for advanced electronics.

Achieving a high power factor and low lattice thermal conductivity is crucial for improving the thermoelectric performance. The eco-friendly Cu12Sb4S13 tetrahedrite inherently exhibits a high power factor (∼10-14 μW cm-1 K-2) and low thermal conductivity (0.5-1.00 W m-1 K-1), but these properties also impose significant limitations for further performance enhancement. To overcome these challenges, researchers have explored strategies such as codoping/synergistic element doping and nanocomposites. In this work, we demonstrate that Sn doping at the Sb site in Cu12Sb4S13 (without the use of nanocomposites) enables the synergistic modulation of both the electronic and thermal properties. The Sn doping increases the hole concentration and enhances the density of states (DOS), leading to a marked improvement in the power factor (at 750 K), 12 μW cm-1 K-2 for x = 0 to 16 μW cm-1 K-2 for x = 0.04. Simultaneously, Sn doping induces strong phonon scattering, which lowers thermal conductivity by ∼69% (at 750 K). This synergistic modulation of the electronic structure, DOS, and scattering mechanisms results in a significant enhancement in the thermoelectric performance. The optimized Cu12Sb3.96Sn0.04S13 sample exhibits an exceptional figure of merit (ZT) of 1.26 at 750 K, representing a 126% increase compared to pristine Cu12Sb4S13. These findings demonstrate the effectiveness of Sn doping in simultaneously optimizing the electrical and thermal properties of Cu12Sb4S13 through the synergistic modulation of the electronic structure, density of states, and phonon scattering mechanisms.

Enhancing the thermoelectric performance of Cu–Ni alloys by introducing carbon nanotubes

Enhanced thermoelectric properties of Cu2-xSe by coordinating carrier concentration to reduce thermal conductivity

For efficient thermoelectric materials, high power factor and low lattice thermal conductivity are desired properties. Therefore, the high lattice thermal conductivity of two-dimensional materials limits their usage in thermoelectric applications. We employ first-principles calculations along with semiclassical Boltzmann transport theory for the electron and phonon dynamics to investigate the thermoelectric properties of nonmetal-shrouded monolayer Ag2S. We show that the simultaneous presence of flat and dispersive bands in the vicinity of the conduction band edge leads to a high power factor, while close proximity of the acoustic and optical bands in the phonon dispersion results in low thermal conductivity. With moderate electron doping, a high in-plane thermoelectric figure of merit is achieved. Our results demonstrate great potential of nonmetal-shrouded monolayer Ag2S in thermoelectric applications.

Enhancing thermoelectric properties of monolayer GeSe via strain-engineering: A first principles study

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The search for new energy harvesting materials that directly convert (waste) heat into electricity has received increasing attention. Transition metal oxides are a promising class of thermoelectric (TE) materials that can operate at high temperature due to their chemical and thermal stability. However, the high lattice thermal conductivity, poor electrical conductivity, and low thermopower have significantly impeded their applications to date. Using first-principles calculations, we predict a known oxide Bi2PdO4 to be a highly efficient hole-doped TE material with low lattice thermal conductivity and high power factor. These properties are due to (i) the strong anharmonicity stemming from Bi3+ 6s2 lone pair electrons (leading to low lattice thermal conductivity) and (ii) the flat-and-dispersive valence band structure with high band degeneracy originating from the localized Pd2+ dz2 orbitals in the stacked square planar ligand field (leading to a large power factor). Our results highlight the possibility of oxides as potential TE materials and also afford a novel strategy of designing TE materials by synthesizing compounds which combine a lone pair active cation with a d8 cation in a stacked square planar ligand field.

Oxides have many potentially desirable characteristics for thermoelectric applications, including low cost and stability at high temperatures, but thus far there are few known high zT n-type oxide thermoelectrics. In this work, we use high-throughput first principles calculations to screen transition metal oxides, nitrides, and sulfides for candidate materials with high power factors and low thermal conductivity. We find a variety of promising materials, and we investigate these materials in detail in order to understand the mechanisms that cause them to have high power factors. These materials all combine a high density of states near the Fermi level with dispersive bands, reducing the trade-off between the Seebeck coefficient and the electrical conductivity, but they do so for several different reasons. In addition, our calculations indicate that many of our candidate materials have low thermal conductivity.

Thermoelectric properties of B-doped nanostructured bulk diamond with lowered thermal conductivity

Experimental investigation on copper foam/hydrated salt composite phase change material for thermal energy storage

The Sulawesi Sea and Sulawesi Island are located in the western Pacific area where volcanic activity, plate subduction, and seismic activity are very active. The Sulawesi basin formed during the Middle Eocene-Late Eocene and nearly half of the Eocene oceanic crust has subducted below the North Sulawesi Trench. The Sulawesi Island was spliced and finalized in the Early Pliocene-Pleistocene during volcanic activity and is recently very active. This area is an optimal location to study volcanic geothermal conditions and subduction initiation mechanisms in the southern part of the western Pacific plate margin, which are important in geothermal and geodynamic research. In this study, we combined 133 heat flow data with gravity and magnetic data to calculate the Moho structure and Curie point depth of the Sulawesi Sea and periphery of the Sulawesi Island, and analyze the distribution characteristics of the geothermal gradient and thermal conductivity. The results show that the average depths of the Moho and Curie surfaces in this area are 18.4 and 14.3 km, respectively, which is consistent with the crustal velocity layer structure in the Sulawesi Basin previously determined by seismic refraction. The average geothermal gradient is 4.96°C (100 m)−1. The oceanic area shows a high geothermal gradient and low thermal conductivity, whereas the land area shows a low geothermal gradient and high thermal conductivity, both of which are consistent with statistical results of the geothermal gradient at the measured heat flow points. The highest geothermal gradient zone occurs in the transition zone from the Sulawesi Sea to Sulawesi Island, corresponding to the spreading ridge of the southward-moving Sulawesi Basin. Comprehensive gravity, magnetic, and geothermal studies have shown a high crustal geothermal gradient in the study area, which is conducive to the subduction initiation. The northern part of the Palu-koro fault on the western side of Sulawesi is likely the location where subduction initiation is occurring. During the process of moving northwest, the northern and eastern branches of Sulawesi Island have different speeds; the former is slow and the latter is fast. These branches also show different deep tectonic dynamic directions; the northern branch tilts north-up and the eastern branch tilts north-down.

Thermoelectric materials convert thermal energy into electrical energy and can be a solution for the global climate crisis. For advanced thermoelectric applications, the conversion efficiency has to be high, motivating the search for materials with a high average thermoelectric figure of merit. To achieve such large thermoelectric figures of merit, the electronic properties must be maximized, and the thermal transport must be minimized over a wide temperature range. The chalcopyrite CuGaTe2 exhibits promising electronic properties but suffers from poor thermoelectric performance due to its high lattice thermal conductivity. In the present study, we perform compressive sensing lattice dynamics (CSLD) and ShengBTE calculations, which suggest that the high room temperature lattice thermal conductivity is a result of high longitudinal group velocities. To effectively reduce the thermal conductivity, we introduce lithium into three variants of CuGaTe2: pristine, Sb-doped, and Ag-doped. All compositions exhibited a significant reduction in the lattice thermal conductivity with the inclusion of lithium without any compromise to the electronic properties. By comparing the elastic moduli, we demonstrate that the reduction in the lattice thermal conductivity is to some extent the result of phonon softening. The low thermal conductivity and high power factor in Cu0.90Li0.05Ag0.05GaTe2 lead to a 56% increase in the average zT compared to the pristine sample. Due to the low cost of lithium, this approach can be adapted to chalcopyrite compounds and other thermoelectric systems to develop sustainable and affordable applications for waste heat recovery.

High temperature abradable sealing coating for SiCf/SiC ceramic matrix composites