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Theoretical calculations on the lattice thermal conductivity (LTC) of the bulk bismuth (Bi) and nanowires (NWs) have been studied with diameters 98 nm, 115 nm and 327 nm in the 〈110〉 direction from temperature range of 0 to 300 K. Several size dependent parameters are estimated to correlate the value of LTC using the modified Morelli-Callaway model, including mass density, Umklapp, normal, boundary impurity, dislocation, and phonon-electron scattering rate. In a particular range of temperature, their effects are varied on the bell-shaped LTC. In accordance, Grüneisen parameter has been calculated for each case and the obtained values fitted with the experimental data of LTC. The result indicates that the impact of increasing the surface area to volume ratio is satisfied on the LTC for some Bi NWs. At a specific temperature, the LTC drops with the reduction of size of NWs. The effects of the variation in size on LTC are calculated and the obtained results are in good agreement with the experimental data.

Transition metal disulfides (TMDCs) have attracted extensive attention in recent years for their novel physical and chemical properties. Based on the first-principles calculations together with semi-classical Boltzmann transport theory, we explored the electronic structures and transport properties of van der Waals WSe2/WTe2 heterostructure. WSe2/WTe2 heterostructure has distinctive hexagon structure and isotropic thermal transport properties. To prove the accuracy of band structure, both Perdew–Burke–Eruzerhof (PBE) and Heyd–Scuseria–Ernzerhof (HSE06) have been used to calculate the band structures. We simulated the band structures under uniaxial and biaxial strains from −8% to +8% and found that all band gaps calculated by HSE06 are larger than results calculated by PBE. More importantly, it was found that when the biaxial strain reaches ±8%, it undergone semiconductor to metal and the dynamic stabilities of WSe2/WTe2 heterostructure have been predicted at the same time. We calculated the mobilities of electrons and holes and found that the mobility of holes is larger than that of electrons. The obtained lattice thermal conductivity (LTC) of WSe2/WTe2 heterostructure at room temperature (70.694 W/mK) is significantly higher than other transition metal tellurium and transition metal selenium, such as PdSe2 (2.91 W/mK) and PdTe2 (1.42 W/mK) monolayers. Our works further enrich studies on the strain dependence of electronic structures and predicted high LTC of WSe2/WTe2 heterostructure, which provide the theoretical basis for experiments in the future. [ABSTRACT FROM AUTHOR]

Buckled hexagonal CSe nanosheet made of earth-abundant elements is investigated for thermoelectric performance by employing the first-principle calculations and the Boltzmann transport theory. The buckled hexagonal CSe sheet is shown to be an indirect-gap semiconductor with a lattice constant of 3.07 Å and band gap of 1.51 eV. The maximum power factor of n-type (p-type) CSe sheet is 618 to 483 (9.87 to 7.42) mW m - 1 K - 2 at the temperatures from 300 to 700 K at the carrier concentration of about 1.17 × 10 13 ( 1.24 × 10 13 ) cm - 2 ). The lattice thermal conductivity of the buckled CSe sheet is in the range of 11.62 to 5.00 W m - 1 K - 1 , and the dimensionless figure of merit of n-type (p-type) CSe sheet is as high as 0.69 to 0.85 (0.18 to 0.40) at the temperatures from 300 to 700 K by choosing appropriate doping level. The high thermoelectric performance indicates that the buckled hexagonal CSe sheet is a promising n-type two-dimensional thermoelectric material. [ABSTRACT FROM AUTHOR]

The rational synthesis of high‐performance thermoelectric (TE) materials guided by theoretical design is still in its infancy. Here by computationally exploiting the possibilities of materials' dopability and hence the electron–phonon transport/scattering, a new defective compound, AgGaTe2, with simultaneous Ag deficiency and isoelectronic substitution of In on Ga‐site (InGa) is predicted, and its high performance is then confirmed via experiments. Using density functional theory and density functional perturbation theory calculations, it is identified that controlled defects viz. Ag vacancy and In substitution in AgGaTe2 system can lead to extremely low lattice thermal conductivity (κL) of around 0.13 WK−1 m−1 at 850 K. This ultralow κL results from both the Ag vacancy that serves as a better rattler and the extra phonon scattering due to the defect induced internal lattice distortion (ψ). The synthesized compounds Ag0.85Ga1−xInxTe2 (x = 0–0.3) indeed achieve the extremely low κL (0.08 WK−1 m−1 for x = 0.15). As a result, the highest TE figure of merit (ZT) of 1.44 is obtained, which is the highest recorded value for silver‐based ternary chalcopyrite semiconductors to date. [ABSTRACT FROM AUTHOR]

Summary: Energy harvesting along with the thermoelectric materials has been investigated over recent decades with increased interest. This is not only due to their structural capability for demonstrating and integrating various new concepts to enhance the thermoelectric figure of merit but also high thermal stability, which is useful for thermoelectric devices. In the present investigation, we have used density functional theory combined with Boltzmann transport scheme to predict the properties of Co2XAl (X = Zr, Nb, Hf) Heuslers. The elastic parameters are simulated to determine the strength and ductile nature of these materials. Three different methods for exchange correlations are utilized to investigate the band profile for that modified Becke‐Johnson potential illustrates the better results than generalized gradient approximation and GGA + U functional. The band profile found to be n‐type (indirect band‐gap) for Co2NbAl and p‐type (direct band‐gap) for Co2ZrAl and Co2HfAl Heuslers near the Fermi level. The formation and cohesive energy approve the thermodynamic stability of these materials. The band occupation and density of states in the post DFT treatment are used to predict the relations among various transport properties. The most important lattice portion of thermal conductivity has been keenly determined by Slack's equation. The half‐metallic nature along with efficient thermoelectric parameters, including electrical conductivity, Seebeck coefficient, thermal conductivity, power factor, and zT suggest the likelihood of these materials to have a potential application in designing the shape of memory devices and imminent thermoelectric and energy harvesting materials. [ABSTRACT FROM AUTHOR]

Rare‐earth pyrochlore materials are promising thermal barrier coatings materials and fundamental understanding of their thermal transport is crucial for further improving its performance. In this work, using density functional theory (DFT) method, we calculated the intrinsic lattice thermal conductivities κl of Ln2Sn2O7 (Ln = La, Gd) and conducted a comprehensive analysis on the mode thermal conductivity, relaxation time, Grüneisen parameters, group velocity, and specific heat, respectively. It is shown that in pyrochlore‐type materials the number of the optical phonons is much larger than that of the acoustic phonon, and the thermal conductivity of acoustic phonons are suppressed, both of which increase the contribution ratio of optical phonons. Especially, through cumulative κl analysis, we found that the contribution of optical phonons is significant: the ratio of optical contribution is more than 50% and 64% in La2Sn2O7 and Gd2Sn2O7. This work provides a comprehensive picture illustrating the significant role of the optical phonons in the lattice thermal conduction in rare‐earth pyrochlore materials, and points out an avenue to obtain low thermal conductivity in complex structural thermal insulation materials. [ABSTRACT FROM AUTHOR]

Silicon-germanium (SiGe) alloys are prominent high-temperature thermoelectric (TE) materials used as a powering source for deep space applications. In this work, we employed rapid cooling rates for solidification by melt-spinning and rapid heating rates for bulk consolidation employing spark plasma sintering to synthesize high-performance p-type SiGe nano-alloys. The current methodology exhibited a TE figure-of-merit (ZT) ≈ 0.94 at 1123 K for a higher cooling rate of ∼3.0 × 107 K/s. This corresponds to ≈ 88% enhancement in ZT when compared with currently used radioisotope thermoelectric generators (RTGs) in space flight missions, ≈ 45% higher than pressure-sintered p-type alloys, which results in a higher output power density, and TE conversion efficiency (η) ≈ 8% of synthesized SiGe nano-alloys estimated using a cumulative temperature dependence (CTD) model. The ZT enhancement is driven by selective scattering of phonons rather than of charge carriers by the high density of grain boundaries with random orientations and induced lattice-scale defects, resulting in a substantial reduction of lattice thermal conductivity and high power factor. The TE characteristics of synthesized alloys presented using the constant property model (CPM) and CTD model display their high TE performance in high-temperature regimes along with wide suitability of segmentation with different mid-temperature TE materials. [ABSTRACT FROM AUTHOR]

A heat flow switching device was developed using semiconductors characterized by very small lattice thermal conductivity. We selected Ag2Ch (Ch = S, Se) which possesses semiconducting electron transport properties and very small lattice thermal conductivity, and tried to control their electron thermal conductivity using bias voltage. The samples were prepared by means of self-propagating high-temperature synthesis under vacuum atmosphere, and mechanically rolled into ribbons of 10µm in thickness. For making the capacitor-type device, amorphous Si and Mo were deposited on the rolled films using RF-sputtering. We compared thermal conductivity with and without bias voltage by means of the AC heating method. As a result, we succeeded in observing a 10% increase of heat flow in the capacitor type heat flow switching device. [ABSTRACT FROM AUTHOR]

Here, we combined Cd and In codoping with a simple hydrothermal synthesis method to prepare SnSe powders composed of nanorod-like flowers. After spark plasma sintering, its internal grains inherited well the morphological features of the precursor, and the multiscale microstructure included nanorod-shaped grains, high-density dislocations, and stacking faults, as well as abundant nanoprecipitates, resulting in an ultralow thermal conductivity of 0.15 W m -1 K -1 for the synthesized material. At the same time, Cd and In synergistically regulated the electrical conductivity and Seebeck coefficient of SnSe, leading to an enhanced power factor. Among them, Sn 0.94 Cd 0.03 In 0.03 Se achieved a peak ZT of 1.50 parallel to the pressing direction, representing an 87.5% improvement compared with pure SnSe. Notably, the material possesses isotropic ZT values parallel and perpendicular to the pressing direction, overcoming the characteristic anisotropy in thermal performance observed in previous polycrystalline SnSe-based materials. Our results provide a new strategy for optimizing the performance of thermoelectric materials through structural engineering.

The present paper is primarily focused to understand the strain driven alterations in thermoelectric (TE) properties of two-dimensional SiH and GeH monolayers from first-principle calculations. Electronic band structures and the associated TE properties of the compounds under ambient and external strains have been critically unveiled in terms of Seebeck coefficients, electrical conductivities, power factors and electronic thermal conductivities. The phonon dispersion relations have also been investigated to estimate the lattice thermal conductivities of the systems. The TE figure of merits of SiH and GeH monolayers under ambient and external strains have been explored from the collective effects of their Seebeck coefficients, electrical conductivities, electronic and lattice thermal conductivities. The present study will be helpful in exploring the strain induced TE responses of SiH and GeH compounds which in turn may bear potential applications in clean and global energy conservation., (© 2024 IOP Publishing Ltd.)

Room-temperature superconductivity has been attracting increasing attention in recent years. Recent studies have proved the potential of compressed H-rich materials for achieving room-temperature superconductivity. In this paper, we study the phononic thermal transport in the rare earth yttrium hydrides allotropes under 0, 50, and 300 GPa by using Boltzmann transport equation. We find that the lattice thermal conductivity of yttrium hydrides increases with the pressure among different allotropes, which is attributed to the increase of bond strength and the decrease of phonon-phonon scattering due to structural compression. Yttrium hydrides structure at high pressure of 300 GPa is the superconducting phase, and has high thermal conductivity around 1,360 Wm−1K−1 at room temperature. Comparison of phonon properties with existing high thermal conductivity materials further uncovers the origin for the observed high thermal conductivity. For the zero pressure allotrope, a large number of optical flat bands mix with the low-frequency acoustic phonons, which significantly increases the phonon scattering channel and effectively suppresses the phonon lifetime. As for yttrium hydrides allotropes under 50 and 300 GPa, there are two obvious band gaps in the phonon dispersion relation, and the band gap of the structure at 300 GPa is significantly wider. The occurrence of the band gap effectively inhibits the absorption and emission process of the three-phonon interactions, leading to the decrease of phonon scattering and thus the increase of the phonon lifetime and thermal conductivity at high pressure. Our work reveals the physical mechanism of the thermal transport behaviors in yttrium hydrides structures under different pressures.

Abstract Charge and thermal transport in a crystal is carried by free electrons and phonons (quantized lattice vibration), the two most fundamental quasiparticles. Above the Debye temperature of the crystal, phonon‐mediated thermal conductivity (κL) is typically limited by mutual scattering of phonons, which results in κL decreasing with inverse temperature, whereas free electrons play a negligible role in κL. Here, an unusual case in charge‐density‐wave tantalum disulfide (1T‐TaS2) is reported, in which κL is limited instead by phonon scattering with free electrons, resulting in a temperature‐independent κL. In this system, the conventional phonon–phonon scattering is alleviated by its uniquely structured phonon dispersions, while unusually strong electron‐phonon (e‐ph) coupling arises from its Fermi surface strongly nested at wavevectors in which phonons exhibit Kohn anomalies. The unusual temperature dependence of thermal conduction is found as a consequence of these effects. The finding reveals new physics of thermal conduction, offers a unique platform to probe e‐ph interactions, and provides potential ways to control heat flow in materials with free charge carriers. The temperature‐independent thermal conductivity may also find thermal management application as a special thermal interface material between two systems when the heat conduction between them needs to be maintained at a constant level.

Thermoelectric (TE) materials can convert waste heat into electrical energy, which has attracted great interest in recent years. In this paper, the effect of biaxial-tensile strain on the electronic properties, lattice thermal conductivity, and thermoelectric performance of α-phase Se2Te and SeTe2 monolayers are calculated based on density-functional theory and the semiclassical Boltzmann theory. The calculated results show that the tensile strain reduces the bandgap because the bond length between atoms enlarges. Moreover, the tensile strain strengthens the scatting rate while it weakens the group velocity and softens the phonon model, leading to lower lattice thermal conductivity kl. Simultaneously, combined with the weakened kl, the tensile strain can also effectively modulate the electronic transport coefficients, such as the electronic conductivity, Seebeck coefficient, and electronic thermal conductivity, to greatly enhance the ZT value. In particular, the maximum n-type doping ZT under 1% and 3% strain increases up to six and five times higher than the corresponding ZT without strain for the Se2Te and SeTe2 monolayers, respectively. Our calculations indicated that the tensile strain can effectively enhance the thermoelectric efficiency of Se2Te and SeTe2 monolayers and they have great potential as TE materials.

Lattice thermal conductivity can be reduced by introducing point defect, grain boundary, and nanoscale precipitates to scatter phonons of different wave‐lengths, etc. Recently, the effect of electron–phonon (EP) interaction on phonon transport has attracted more and more attention, especially in heavily doped semiconductors. Here the effect of EP interaction in n‐type P‐doped single‐crystal Si has been investigated. The lattice thermal conductivity decreases dramatically with increasing P doping. This reduction on lattice thermal conductivity cannot be explained solely considering point defect scattering. Further, the lattice thermal conductivity can be fitted well by introducing EP interaction into the modified Debye–Callaway model, which demonstrates that the EP interaction can play an important role in reducing lattice thermal conductivity of n‐type P‐doped single‐crystal Si. [ABSTRACT FROM AUTHOR]

The presence of water in minerals generally alters their physical properties. Ringwoodite is the most abundant phase in the lowermost mantle transition zone and can host up to 1.5–2 wt% water. We studied high‐pressure lattice thermal conductivity of dry and hydrous ringwoodite by combining diamond‐anvil cell experiments with ultrafast optics. The incorporation of 1.73 wt% water substantially reduces the ringwoodite thermal conductivity by more than 40% at mantle transition zone pressures. We further parameterized the ringwoodite thermal conductivity as a function of pressure and water content to explore the large‐scale consequences of a reduced thermal conductivity on a slab's thermal evolution. Using a simple 1‐D heat diffusion model, we showed that the presence of hydrous ringwoodite in the slab significantly delays decomposition of dense hydrous magnesium silicates, enabling them to reach the lower mantle. Our results impact the potential route and balance of water cycle in the lower mantle. Plain Language Summary: The physical properties of minerals are determined by the interaction of atoms in the crystal lattice. Water can be incorporated into the crystal structure and alter its behavior. Ringwoodite is a high‐pressure mineral that can host large quantities of water and is expected to be abundant in the lower part of Earth's mantle transition zone, a region ranging from 520 to 660‐km depth. Here we studied ringwoodite thermal conductivity, describing how effectively heat is transported through solids. Based on our measurements we determined that water in ringwoodite significantly slows down heat propagation. We performed computer simulations to investigate the large‐scale implications of our findings. For this purpose, we modeled a cold oceanic plate, entirely made of ringwoodite, which is surrounded by warm mantle. The delayed heat transport is sufficient to maintain low temperatures in the inner part of the oceanic plate and potentially preserve the hydrous minerals for an extended period of time. Key Points: Ringwoodite thermal conductivity is reduced by 40% due to the presence of 1.73 wt% water in the crystal structureLower thermal conductivity of hydrous ringwoodite might delay the breakdown of hydrous phases hosted in a subducting slabHydrous ringwoodite acts as a heat propagation barrier, supporting preservation of hydrous minerals down to the lower mantle [ABSTRACT FROM AUTHOR]

Polycrystalline bulks of Hf-doped Cu0.01Bi2Te2.7Se0.3 are prepared via a conventional melt-solidification process and subsequent spark plasma sintering technology, and their thermoelectric performances are evaluated. To elucidate the effect of Hf-doping on the thermoelectric properties of n-type Cu0.01Bi2Te2.7Se0.3, electronic and thermal transport parameters are estimated from the measured data. An enlarged density-of-states effective mass (from ~0.92 m0 to ~1.24 m0) is obtained due to the band modification, and the power factor is improved by Hf-doping benefitting from the increase in carrier concentration while retaining carrier mobility. Additionally, lattice thermal conductivity is reduced due to the intensified point defect phonon scattering that originated from the mass difference between Bi and Hf. Resultantly, a peak thermoelectric figure of merit zT of 0.83 is obtained at 320 K for Cu0.01Bi1.925Hf0.075Te2.7Se0.3, which is a ~12% enhancement compared to that of the pristine Cu0.01Bi2Te2.7Se0.3. [ABSTRACT FROM AUTHOR]

Self‐consistent ab‐initio calculations with highly precise spin‐polarized, density functional theory have been performed for the first time, to investigate the electronic structure, magnetism, transport, elasto‐mechanical, and thermophysical properties of newly tailored Mn‐based full‐Heuslers. The cohesive and ground‐state energy calculations in ferromagnetic, nonmagnetic, and antiferromagnetic states confirm the stability of materials in face‐centered ferromagnetic configuration. The spin‐based band structure analysis is well defined by modified Becke‐Johnson potential with the occurrence of half‐metallic character along the Fermi level. Estimation of elastic parameters is used to check the mechanical stability and nature of forces occurring in materials, where we see the alloys display ductile nature along with a Debye temperature of 398.75 K for Mn2NbAl, 337.53 K for Mn2NbGa, and 360.52 K for Mn2NbIn. Furthermore, within the solution of Boltzmann theory, thermoelectric efficient parameters address its applications in energy harvesting and solid‐state device applications. Thermodynamic potentials have been keenly predicted by implementing quasi harmonic Debye model to descript its stability at high temperature and pressure varying conditions. The prediction of ground state and thermodynamic properties from extensive first‐principles calculations could be beneficial for its future experimental insights with intriguing applications. Hence, the overall theme from the current study creates an application stand in spintronics, power generation, as well as green energy sources for future technologies. [ABSTRACT FROM AUTHOR]

Recent progress in theoretical mineral physics based on the ab initio quantum mechanical computation method has been dramatic in conjunction with the rapid advancement of computer technologies. It is now possible to predict stability, elasticity, and transport properties of complex minerals quantitatively with uncertainties that are comparable to or even smaller than those attached in experimental data. These calculations under in situ high-pressure (P) and high-temperature conditions are of particular interest because they allow us to construct a priori mineralogical models of the deep Earth. In this article, we briefly review recent progress in studying high-P phase relations, elasticity, thermal conductivity, and rheological properties of lower mantle minerals including silicates, oxides, and some hydrous phases. Our analyses indicate that the pyrolitic composition can describe Earth's properties quite well in terms of density and P- and S-wave velocity. Computations also suggest some new hydrous compounds that could persist up to the deepest mantle and that the postperovskite phase boundary is the boundary of not only the mineralogy but also the thermal conductivity. ▪ The ab initio method is a strong tool to investigate physical properties of minerals under high pressure and high temperature. ▪ Calculated thermoelasticity indicates that the pyrolytic composition is representative to the chemistry of Earth's lower mantle. ▪ Simulations predict new dense hydrous phases stable in the whole lower mantle pressure and temperature condition. ▪ Calculated lattice thermal conductivity suggests a heat flow across the core mantle boundary no greater than 10 TW. [ABSTRACT FROM AUTHOR]

In thermal barrier coating materials, there are several conventional routes to suppress the lattice thermal conductivity in order to improve the thermal insulation efficiency, such as doping, increasing the mass of unit cells, or using complex lattice structures. However, in spite of the fact that the mass of unit cell of La 2 Sn 2 O 7 is much larger than that of La 2 Zr 2 O 7 and these two pyrochlores have very similar crystal structure, the thermal conductivity of the former is much higher. By comparing the phonon spectra, phonon density of states and Grüneisen parameter of each phonon mode calculated using first-principles methods, it is found that the La 2 Zr 2 O 7 has stronger anharmonicity than La 2 Sn 2 O 7 because of the anharmonic potential of La atoms in the (111) plane. The difference between La potentials of the two pyrochlores is attributed to the fact that the electron cloud around Zr atoms is more easily polarized than that around Sn by the displacement of La atoms, which induces stronger long-range interaction and decreases the potential energy of La. These results provide intuitive insights towards the interplay between the electronic structure, anharmonicity and lattice thermal conductivity of rare-earth pyrochlores. [ABSTRACT FROM AUTHOR]

Boron-based 2D materials are of current interest. However, graphene-like geometry is unstable for B due to the electron deficiency, which can be stabilized by introducing H, F and Cl. Here, using density functional theory combined with phonon Boltzmann transport equation, we perform systematic studies on how the functionalization changes the lattice thermal conductivity (LTC). We find that when going from hydrogenation to fluorination and chlorination, the LTC along zigzag direction changes from 367.6 to 211.3 and 43.0 W/(m·K), while the corresponding values in armchair direction are 279.6, 198.9, and 41.6 W/(m·K), respectively. These huge differences imply the sensitivity of LTC to functionalization, which can be attributed to the enhanced anharmonicity as revealed by analyzing group velocity, Gruneisen parameter, anharmonic scattering rates, and three-phonon scattering space. [ABSTRACT FROM AUTHOR]

Summary: The origin of half‐metallicity, structural, thermoelectric, elasto‐mechanical, and thermodynamic properties of Co2ScSb and Co2TiSb full‐Heuslers has been examined by full potential methods. Structural optimizations support the stability of both alloys in AlCu2Mn‐prototype with space symmetry of Fm3¯m (#225) space group. The occurrence of perfect band occupation and interpretation of density of states through the modified version of the Becke Johnson (mBJ) scheme for both these Heusler systems delivers more precise and accurate results rather than GGA and GGA + U. The density of states and band occupation describes the semiconducting nature with an indirect band‐gap 1.08 eV for Co2ScSb and 1.32 eV Co2TiSb. Robustness of various elastic constants against external forces is checked to descripted stability of these alloys. The evaluation of elastic constants and its other associated mechanical constituents reveals ductile behavior along with high melting temperature. The thermoelectric coefficients are used to check the applicability of the material for waste heat recovery systems and technological purposes. Thermal parameters support the material's low anharmonicity and hence predict the stability of these alloys at the wide range of temperatures and pressure. The thermoelectric parameters pose its applications and stand to develop devices based on spintronics and thermoelectric purposes. [ABSTRACT FROM AUTHOR]

Nanoparticles in thermoelectric alloys has been considered as one of the most important ingredients to enhance their thermoelectric figure of merit zT mainly by reducing the lattice thermal conductivity due to intensified phonon scattering. However, the scattering mechanism of phonon with respect to wavelengths, which provides the comprehensive design rules for nanocomposites with enhanced zT , has not been fully understood. Here, we report a critical role of nanoparticles for the lattice thermal conductivity reduction from the theoretical and experimental analysis of the temperature-dependent thermal and electronic transport properties of p -type Ag/Cu nanoparticles-embedded Bi 0.5 Sb 1.5 Te 3 with respect to their electronic, bipolar, and lattice thermal conductivities. It was found that the introduction of the Ag/Cu nanoparticles reduced the lattice thermal conductivity through the additional phonon scattering based on the changeover between the Rayleigh and geometrical scatterings, indicating the indispensability of nanoparticles to scatter phonons that cannot be scattered effectively by either point defects or grain boundaries. Image, graphical abstract [ABSTRACT FROM AUTHOR]

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Theoretical calculations are performed on lattice thermal conductivity (LTC) and related parameters for the zinc blende and wurtzite structure of InAs nanowires (NWs) with diameters of 50, 63, 66, 100 and 148 nm through the Morelli–Callaway model. For the model to be efficiently applicable, the longitudinal and transverse modes are considered. The melting point of the various-sized NWs is considered to estimate the Debye and phonon group velocities. The impacts of Grüneisen parameter, dislocations and surface roughness are also successfully utilized to address the calculated and measured LTC of the semiconductor under investigation. Results show that the Grüneisen parameter increases with decreasing NW diameter and that phonon confinement leads to an observable deviation of the calculated LTC curve from that of the experimental one in the case of bulk InAs. We assume that NW boundaries, dislocations and imperfections are responsible for the scattering of phonons along with electrons and other phonons because of normal and Umklapp processes. Therefore, at a specified temperature, LTC depends on the size and crystal structure of the semiconductor. As such, the thermal and mechanical parameters of InAs can be greatly modified by decreasing the size and dimension of the semiconductor as a result of the quantum-confinement effect. [ABSTRACT FROM AUTHOR]

The figure of merit of thermoelectric materials can be increased by suppressing the lattice thermal conductivity without degrading electrical properties. Phonons are the carriers for lattice thermal conduction, and their transport can be impeded by nanostructuring, owing to the recent progress in nanotechnology. The key question for further improvement of thermoelectric materials is how to realize ultimate structure with minimum lattice thermal conductivity. From spectral viewpoint, this means to impede transport of phonons in the entire spectral domain with noticeable contribution to lattice thermal conductivity that ranges in general from subterahertz to tens of terahertz in frequency. To this end, it is essential to know how the phonon transport varies with the length scale, morphology, and composition of nanostructures, and how effects of different nanostructures can be mutually adopted in view of the spectral domain. Here we review recent advances in analyzing such spectral impedance of phonon transport on the basis of various effects including alloy scattering, boundary scattering, and particle resonance. [ABSTRACT FROM AUTHOR]

Thermal physical properties of inorganic borates are important in application of optical device working under high temperature. Herein, we investigate the temperature-dependent thermoelasticity, thermal expansion(α), and lattice thermal conductivity(κ) of simple orthohomibic LaBO 3 with a two dimension like crystal structure though first principles for the first time. The calculated rate of temperature-dependent second elastic constant C 11 is significantly larger than that of C 22 and C 33 , and the theoretical slopes of corresponding bulk, shear, and Young's moduli in the range of 300–900 K are −0.0289 GPa•K−1, −0.0156 GPa•K−1, and −0.0398 GPa•K−1, respectively. The predicted α is positive and increases with the rise of temperature. The anisotropic ratio α c / α a or α c / α b is approximately 2 at 300 K, which might be attributed to the difference of elastic compliance S 12 and S 13. Besides, the anisotropic lattice thermal conductivity κ a , κ b and κ c of LaBO 3 is predicted to be 1.43, 1.40 and 0.80 W/m-K at 300 K via Debye-Callaway model. Most importantly, the atomic projected Grüneisen parameters γ reveal that asymmetrical LaO 9 polyhedra in the crystal lattice dominate the thermal expansion and lattice thermal conductivity. Our results indicate that LaBO 3 has good thermal physical properties working under high temperature. [Display omitted] • The thermophysical property of LaBO 3 was predicted by first-principles calculation. • The thermal expansion coefficients along c direction are much larger than those of a and b directions. • The anisotropic lattice thermal conductivity is predicted by Debye-Callaway model. • The lattice thermal conductivity along c direction is smaller than that of a and b directions. • The projected atomic Grüneisen parameters suggest that LaO 9 polyhedron charge the thermophysical properties in LaBO 3. [ABSTRACT FROM AUTHOR]

We applied the density functional theory formalism to compute the lattice thermal conductivity, transport and thermoelectric properties of Rb 2 LiTlF 6 double perovskite in the cubic phase. To gain some insights on lattice related dynamic behaviour of this material, we determined its phonon lifetimes and Grüneisen parameters within the considered frequency range. This quaternary compound has a very low value of lattice thermal conductivity, with the predicted value of 0.687 W/mK at 300 K. The highest value of dimensionless figure of merit was determined to be 5.73 × 10−3 at 800 K when hole concentration is 1020 cm−3, this low ZT value could be attributed to the wide band gap nature of this compound. Our results will serve as a benchmark for future experimental and theoretical research on lattice and thermoelectric properties of this material. • Lattice dynamics. • Transport properties. • Thermoelectric figure of merit. [ABSTRACT FROM AUTHOR]

The lattice thermal conductivity of the CdO monolayer was investigated by density functional theory in combination with Boltzmann transport theory and it was estimated about 3.346 Wm−1K−1 at T = 300 K. Comparing this result with the one reported for the bulk CdO, it was revealed that the lattice thermal conductivity of the monolayer is lower than the bulk CdO. The lower lattice thermal conductivity of the CdO monolayer was attributed to the lower phonon lifetime and phonon group velocity in comparison to the bulk counterpart. Considering the lower lattice thermal conductivity of the monolayer, higher thermoelectric efficiency was estimated in comparison with the reported efficiency for the bulk CdO. At T = 900 K, the maximum zT = 0.76 can be found in p-type for the hole concentrations of 7.2 × 1012 cm−2. • The phonon dispersion of CdO monolayers were investigated with considering Born effective charges. • The contribution of phonon frequency to the k lat , group velocity, and phonon lifetime were investigated. • Thermoelectric efficiency of the CdO monolayer was investigated. [ABSTRACT FROM AUTHOR]

Bismuth sulphide is one of the promising thermoelectric material due to its low thermal conductivity, less toxicity, and abundance in nature. This work analyzed an Al-substituted Bi 2 S 3 compounds for mid-temperature thermoelectric applications prepared by hydrothermal route. The combination of stacking faults and point defects significantly improved the phonon scattering, resulting in decreased thermal conductivity in (x = 0.10) Al substituted sample with the value of 0.498 Wm−1K−1 at 623 K. Also, it simultaneously contributes to the enhancement in carrier concentration of −2.15 × 1019 cm−3, resulting the increased electrical conductivity of 10,142 Sm-1 at 563 K. Further, x = 0.025 Al substitution in Bi 2-x Al x S 3 leads to a high power factor of 338 Wm−1K-2 and a low phonon thermal conductivity of 0.578 μWm−1K−1, leading to a maximum zT of 0.30 at 623 K. [Display omitted] • Al substituted Bi 2 S 3 were prepared by the one-pot hydrothermal method followed by Hot press. • The isovalant substitution of Al significantly improves the electrical transport properties by carrier tuning. • Stacking faults and dislocations enhance the multiple phonon scattering results in decreased lattice thermal conductivity. • The (x = 0.025) substituted Bi 2-x Al x S 3 sample achieved a maximum zT of 0.30 at 623 K. [ABSTRACT FROM AUTHOR]

Ternary chalcostibite CuSbSe 2 compound is known for low thermal conductivity. However, the poor electrical properties severely limit its thermoelectric performance. In this study, the Mn-doped CuSb 1- x Mn x Se 2 (x = 0–0.04) samples were synthesized by vacuum melting with spark plasma sintering, and their thermoelectric properties were characterized. The results indicate that the impurity phase Cu 3 SbSe 3 will be generated when Mn content x > 0.02, and the carrier concentration and mobility were optimized significantly for the Mn-doped compounds, thus enhancing the electrical transport performance. In terms of results, the PF increases from 1.3 × 102 to 2.18 × 102 µW m−1 K−2 at 673 K. Point defects and the second phase enhance phonon scattering and lead to a lower lattice thermal conductivity for CuSb 1- x Mn x Se 2 compounds, the κ l decreases from 0.39 to 0.26 W m−1 K−1 at 673 K. As a consequence, a maximum figure of merit ZT of ∼0.53 was achieved at 673 K for CuSb 0.97 Mn 0.03 Se 2 , which is 140 % higher than the intrinsic CuSbSe 2. • Optimization of carrier concentration and mobility improved electric conductivity. • Phonon transport was suppressed resulting in a 32 % decrease for κ l. • The ZT increased by 1.4 times compared with the intrinsic CuSbSe 2. [ABSTRACT FROM AUTHOR]

Using full electron-phonon interactions and the Boltzmann transport equation, the phonon scattering channel and electrical properties of graphene are investigated under anharmonic phonon renormalization (APRN). After the anharmonic phonon renormalization is considered, both phonon frequency and three-phonon phase space become small with the temperature. Meanwhile, the APRN has a greater effect on the acoustic branch and little effect on the optical branch. When three-phonon scattering is considered, the corresponding thermal conductivity is 3518 W/mK (300 K), 1900 W/mK (500 K), and 1122 W/mK (800 K), respectively. After four-phonon scattering is considered, the thermal conductivity of graphene decreases to 1844 W/mK at 300 K, 900 W/mK at 500 K, and 600 W/mK at 800 K, respectively. For three-phonon scattering, the primary scattering channels include ZA + TA → ZO, TA + TA → ZA, LA + LA → ZO, ZA/TA → TA + LA, LA/ZO → ZO + TA, TO → ZA + LA and LO → ZO + LA. About the four-phonon scattering channel, the main contributions originate from X + ZA → ZA + ZA, X + ZA/ZO → ZA + ZO, and X + TA → LA + ZO. The anharmonic phonon renormalization enlarges the strength of electron-phonon coupling, leading to the increase of n-type electric resistance from 24 Ω to 26 Ω at room temperature. This work gives insight into the phonon scattering channel and electrical property via anharmonic phonon renormalization in which normal processes dominate the ph-ph scattering. [Display omitted] 1. The effect of anharmonic phonon renormalization on the thermal/electrical properties of graphene is investigated. 2. When considering the renormalization effect, phonon frequency/phase space become small with the temperature. 3. The anharmonic phonon renormalization has a greater effect on acoustic branch and little effect on optical branch. 4. The primary scattering channels include A + A → A/O, A/O → A/O + A and X + ZA/TA/ZO → ZA/LA + ZA/ZO. • For the four-phonon scattering channel, the main contributions originate from X + ZA/TA/ZO → ZA/LA + ZA/ZO. 5. The anharmonic phonon renormalization enlarges the electron-phonon coupling matrix and electric resistance. [ABSTRACT FROM AUTHOR]

• Cu doping in Cs 2 Cu x Ag 1-x BiBr 6 perovskites alters electronic structure, affecting thermoelectric properties. • The introduction of Cu dopants narrows the band gap and influences the carrier concentration in the material. • Enhanced thermoelectric performance, including improved zT values, observed at specific Cu doping levels. • Temperature-dependent analysis reveals varied peak zT values for different compositions, suggesting tailored applications. This study focuses on examining the thermoelectric properties of Cs 2 Cu x Ag 1-x BiBr 6 perovskites and investigates the influence of lattice thermal conductivity on their thermoelectric performance. To achieve this, the study utilizes a combination of first-principles calculations and Boltzmann transport theory. The calculated structural properties, obtained through the generalized Perdew-Burke-Ernzerhof approximation (GGA-PBE), closely align with both experimental and theoretical data for lattice constants and bulk modulus. The electronic properties were assessed using the TB-mBJ (Tran-Blaha-modified Becke-Johnson) method, indicating relatively small band gaps within the range of 1.146 eV for Cs 2 CuBiBr 6 and 2.072 eV for Cs 2 AgBiBr 6. The materials exhibit significant Seebeck coefficients and controllable lattice thermal conductivity between 0.067 and 0.662 W/mK at room temperature, with the relaxation time being determined using the Drude model. The study revealed that the most significant zT values, approximately 0.80, were observed when x = 0.5 in the Cs 2 Cu x Ag 1-x BiBr 6 perovskite material. This indicates that these perovskites possess the ability to efficiently and inexpensively convert heat into electrical energy. Consequently, these findings propose the potential of Cs 2 Cu x Ag 1-x BiBr 6 perovskites as a favorable option for real-world thermoelectric applications. The study further highlights the importance of utilizing lattice thermal conductivity to enhance the overall thermoelectric performance of such materials. [ABSTRACT FROM AUTHOR]

Improvement of existing material properties is necessary for high-efficiency thermoelectric power conversion, but novel thermoelectric materials must also be predicted and synthesized. Here we solve the phonon Boltzmann transport equation using first-principles computations to examine the lattice thermal conductivity of Janus In 2 Ge 2 Te 3 Se 3 and In 2 Ge 2 Se 6 bilayers. Results show that the frequencies at which larger gaps appear in the intermediate and high-frequency optical branches of In 2 Ge 2 Te 3 Se 3 are lower than those of In 2 Ge 2 Se 6. As a result, the phonon dispersion curve of In 2 Ge 2 Te 3 Se 3 shifts downward. Since Te atoms are heavier than Se atoms, compared to In 2 Ge 2 Se 6 , In 2 Ge 2 Te 3 Se 3 has a lower overall phonon group velocity. Furthermore, the tight coupling of the in-plane acoustic modes and the soft bending of In 2 Ge 2 Te 3 Se 3 in the finite layer thickness coupling result in an increase in the phonon-phonon scattering, a reduction in the phonon relaxation time, and a larger Grüneisen parameter, indicating that In 2 Ge 2 Te 3 Se 3 is more anharmonic. At a temperature of 1000 K, the sum of all these parameters results in a minimum lattice thermal conductivity of 0.05 W/mK for In 2 Ge 2 Te 3 Se 3 and 0.24 W/mK for In 2 Ge 2 Se 6. This study sheds light on the Janus In 2 Ge 2 Te 3 Se 3 and In 2 Ge 2 Se 6 bilayer thermal transport capabilities, it may open the door for achieving thermal conductivity control in applications such as thermal management and thermoelectric devices. • Lattice thermal conductivity of Janus In 2 Ge 2 Te 3 Se 3 and In 2 Ge 2 Se 6 bilayers were investigated using first-principles calculations. • The lattice thermal conductivity of In 2 Ge 2 Te 3 Se 3 is smaller than that of In 2 Ge 2 Se 6 due to the occurrence of larger voids in the intermediate and high frequency optical branches of In 2 Ge 2 Te 3 Se 3 at lower frequencies than In 2 Ge 2 Se 6 , the heavier Te atoms than Se atoms, and the larger Grüneisen parameter • Janus In 2 Ge 2 Te 3 Se 3 and In 2 Ge 2 Se 6 bilayers have the minimum lattice thermal conductivity of 0.05 W/mK and 0.24 W/mK at 1000 K, respectively. [ABSTRACT FROM AUTHOR]

Donor-doped strontium titanate (SrTiO3) is one of the most promising n-type oxide thermoelectric materials. Routine doping of La at Sr site can change the charge scattering mechanism, and meanwhile can significantly increase the power factor in the temperature range of 423–773 K. In addition, the introduction of Sc partially substitutes Sr, thus further increasing the electron concentration and optimizing the electrical transport properties. Moreover, the excess Sc in the form of Sc2O3 composite suppresses multifrequency phonon transport, leading to low thermal conductivity of κ = 3.78 W·m−1·K−1 at 773 K for sample Sr0.88La0.06Sc0.06TiO3 with the highest doping content. Thus, the thermoelectric performance of SrTiO3 can be significantly enhanced by synergistic optimization of electrical transport and thermal transport properties via cation doping and composite engineering.

Although some atomically thin 2D semiconductors have been found to possess good thermoelectric performance due to the quantum confinement effect, most of their behaviors occur at a higher temperature. Searching for promising thermoelectric materials at room temperature is meaningful and challenging. Inspired by the finding of moderate band gap and high carrier mobility in monolayer GeP3, we investigated the thermoelectric properties by using semi-classical Boltzmann transport theory and first-principles calculations. The results show that the room-temperature lattice thermal conductivity of monolayer GeP3 is only 0.43 Wm−1K−1 because of the low group velocity and the strong anharmonic phonon scattering resulting from the disordered phonon vibrations with out-of-plane and in-plane directions. Simultaneously, the Mexican-hat-shaped dispersion and the orbital degeneracy of the valence bands result in a large p-type power factor. Combining this superior power factor with the ultralow lattice thermal conductivity, a high p-type thermoelectric figure of merit of 3.33 is achieved with a moderate carrier concentration at 300 K. The present work highlights the potential applications of 2D GeP3 as an excellent room-temperature thermoelectric material.