Lattice Thermal Conductivity Research Articles

Unraveling the Synergistic Role of Kinks in Zig-Zag Ag2Se Nanorod Arrays for High Room-Temperature zT and Improved Mechanical Properties: Experimental and First-Principles Studies.

Flexible thermoelectric materials are usually fabricated by incorporating conducting or organic polymers; however, it remains a formidable task to achieve high thermoelectric properties comparable to those of their inorganic counterparts. Here, we present a high zT value of 1.29 ± 0.31 at room temperature in the hierarchical zig-zag Ag2Se nanorod arrays fabricated using the glancing angle deposition (GLAD) technique followed by a facile selenization process. The high zT value at 300 K is ascribed to the ultrahigh power factor of 3101 ± 252 μW/m-K2 and the reduced thermal conductivity of 0.72 ± 0.01 W/mK. Based on ab initio computational and experimental evidence, we reveal that kinked Ag2Se nanorod arrays consisting of rough interfaces modulate the lattice thermal conductivity up to 48.5% at room temperature. The modulation results from interchanging of phonon modes at kink points and enhanced scattering from a large number of rough interfaces. Further, benefiting from kinked hierarchy, a notable improvement in the mechanical performance is observed for zig-zag Ag2Se nanorods which is confirmed by nanoindentation measurements. The synergic improvement in thermoelectric and mechanical performance not only unravels a paradigm to harness thermoelectric heat but also offers deeper insights into tuning the mechanical properties of inorganic thermoelectric materials.

A high-throughput framework for lattice dynamics

AbstractWe develop an automated high-throughput workflow for calculating lattice dynamical properties from first principles including those dictated by anharmonicity. The pipeline automatically computes interatomic force constants (IFCs) up to 4th order from perturbed training supercells, and uses the IFCs to calculate lattice thermal conductivity, coefficient of thermal expansion, and vibrational free energy and entropy. It performs phonon renormalization for dynamically unstable compounds to obtain real effective phonon spectra at finite temperatures and calculates the associated free energy corrections. The methods and parameters are chosen to balance computational efficiency and result accuracy, assessed through convergence testing and comparisons with experimental measurements. Deployment of this workflow at a large scale would facilitate materials discovery efforts toward functionalities including thermoelectrics, contact materials, ferroelectrics, aerospace components, as well as general phase diagram construction.

Tl2XY (X, Y = S, Se) monolayers with low lattice thermal conductivity and high thermoelectric performance by full-band approach with four scattering mechanisms

Abstract The low lattice thermal conductivity and high thermoelectric performance of the Janus Tl2SSe monolayer in the temperature region of 300–700 K are identified based on the thermoelectric properties of the Tl2S2, Tl2SSe, and Tl2Se2 monolayers. The transport coefficients for carrier concentrations and temperatures are obtained by solving the linearized Boltzmann transport equation in a full-band electronic structure. Four scattering mechanisms of acoustic deformation potential, optical deformation potential, polar optical phonon, and ionized impurity scatterings are considered. The ionized impurity scattering is recognized as the most important. The lattice thermal conductivity of the Janus Tl2SSe monolayer is substantially smaller than those of the Tl2S2, Tl2Se2 monolayers with higher symmetry. Moreover, we find that the Janus structures of the Tl2SSe monolayer increase the dielectronic constants and enhance the polar optical phonon scattering, then reduce the power factor to some extent. Therefore, the lattice thermal conductivity actually couples with the transport coefficient and cannot be individually regulated as is usually assumed. However, the ZT value of the Tl2SSe monolayer can still reach 1.77 at 700 K even if the intrinsic concentration and the bipolar effect are included. Therefore, the Tl2SSe monolayer is expected to be a promising candidate for thermoelectric materials.

Enhancing the Thermoelectric Performance of n-Type Mg3Sb2-Based Materials via Ag Doping.

The n-type Mg3(Sb, Bi)2 compounds show great potential for wasted heat energy harvesting due to their promising thermoelectric properties. This work discovers that doping transition element Ag into the n-type Mg3(Sb, Bi)2 can effectively optimize the power factor and suppress the lattice thermal conductivity simultaneously. Interestingly, the Ag doping has different effects compared to the isoelectronic and same group element Cu addition studied previously. A high power factor of 19.6µW cm-1 K-2 is obtained at 673K owing to the increased electrical conductivity. At the same time, the lattice thermal conductivity is reduced to ≈0.5W m-1 K-1 because of enhanced phonon scattering induced by Ag atoms. These improvements lead to a peak figure of merit (ZT) of 1.64 at 673K as well as a high average ZT of 1.27 is obtained from 323 K to 673K. Furthermore, a thermoelectric single leg with a competitive conversion efficiency of ≈11% under a hot-side temperature of 673K is fabricated successfully. In addition, a 2-pair module composed of n-type Mg3(Sb, Bi)2 alloy and p-type MgAgSb-based compound demonstrates the high conversion efficiency of ≈7.9% at a temperature difference of 277K, which will significantly upgrade the sustainable energy recycling technology.

High thermolectric properties of disordered Ge0.8-ySn0.2MnyTe semiconductor

For layered GeTe-based materials, the typical strategy to reduce the thermal conductivity of the crystal lattice is to introduce atomic disorder, increase the lattice non-harmonicity, and maximize the fluctuations of the quality/stress field in the sample. Since Sn/Mn can easily form solid solutions in the GeTe matrix, the degree of disorder in the sample is much higher than the level reported in IV-VI alloys in the past, which leads to a strong phonon scattering and a sharp decrease in the lattice thermal conductivity over the entire temperature range. In addition, Mn plays a significant role in changing the valence band structure of GeTe, i.e., Mn doping enhances the convergence of the light valence band and the heavy valence band and the change of the bandgap, significantly increasing the Seebeck coefficient of the GeTe matrix, resulting in a significant improvement in the thermoelectric performance of the Sn/Mn co-doped synthesized GeTe-based materials. Finally, we found that treating the sample with layered disorder is an effective method to improve the thermoelectric performance, and this study has certain reference value for the development of novel toxic-free, high-performance thermoelectric materials.

Origin of Intrinsically Low Lattice Thermal Conductivity in Solids.

Reducing lattice thermal conductivity through external modulation techniques such as defect engineering may potentially interfere with electronic transport. Materials with intrinsically low lattice thermal conductivity have the potential to decouple the control of lattice heat transport and electronic transport, which is of great significance in the field of thermoelectric energy conversion. This paper reviews the origin of intrinsically low lattice thermal conductivity, which is directly related to three physical quantities (heat capacity, phonon group velocity, and phonon relaxation time) and is ultimately reflected in the lattice structure and bonding characteristics. An understanding of the fundamental nature of low lattice thermal conductivity can aid in guiding experimental design and theoretically enabling high-throughput prediction of novel low lattice thermal conductivity materials according to the intrinsic properties.

Valence Band Modification and Enhanced Phonon‐Phonon Interactions for High Thermoelectric Performance in GeTe

AbstractThe strong coupling between carrier and phonon transport in thermoelectric (TE) materials severely limits improvements to the figure of merit (ZT). In this work, an approach is proposed to weaken electron‐phonon coupling, effectively enhancing the TE performance of GeTe. Alloying with Zn4Sb3 reduces excessive carrier concentration (nH), widens the bandgap, and promotes band convergence, synergistically improving charge carrier transport and ensuring a high power factor. Additional Pb doping further optimizes nH, boosting the power factor even more. Moreover, phonon transport is suppressed through Pb doping, as reflected in enhanced acoustic‐optical interactions due to the crossing of optical and acoustic modes, and a reduction in sound group velocity. This reinforced strong phonon scattering, combined with multi‐scale hierarchical nano/microstructures in the matrix, significantly reduces lattice thermal conductivity. As a result, a high ZT of 2.1 is achieved at 753 K in Ge0.9Pb0.1Te+0.9%Zn4Sb3. Alongside optimized mechanical performance, a high power density of 1.46 W cm−2 is realized at a temperature difference of 350 K in the fabricated 7‐pair TE module. The findings demonstrate the effectiveness of a stepwise optimization strategy for developing high‐performance TE materials.

Thermal Conductivity in Biphasic Silicon Nanowires.

The work unravels the previously unexplored atomic-scale mechanism involving the interaction of phonons with crystal homointerfaces. Silicon nanowires with engineered isotopic content and crystal phases were chosen for this investigation. Crystal polytypism, manifested by the presence of both diamond cubic and rhombohedral phases within the same nanowire, provided a testbed to study the impact of phase homointerfaces on phonon transport. The lattice thermal conductivity and its temperature response were found to be markedly different in the presence of polytypism. Its origin, however, was not traced to any acoustic mismatch as the polytypic nanowires presented a similar phonon spectrum as their counterparts. Rather, phenomenological modeling and atomistic simulations identified and quantified the role of atomically rough homointerfaces and the subsequent phonon scattering from such homointerfaces in shaping the phonon behavior. This framework provides the inputs necessary to advance the design and modeling of phonon transport in nanoscale semiconductors.

Oriented Bi2Te3-based films enabled high performance planar thermoelectric cooling device for hot spot elimination

Film-thermoelectric cooling devices are expected to provide a promising active thermal management solution with the continues increase of the power density of integrated circuit chips and other electronic devices. However, because the microstructure-related performance of thermoelectric films has not been perfectly matched with the device configuration, the potential of planar devices on chip heat dissipation has still not been fully exploited. Here, by liquid Te assistant growth method, highly (00 l) orientated Bi2Te3-based films which is comparable to single crystals are obtained in polycrystal films in this work. The high mobility stem from high orientation and low lattice thermal conductivity resulting from excess Te induced staggered stacking faults leads to high in-plane zT values ~1.53 and ~1.10 for P-type Bi0.4Sb1.6Te3 and N-type Bi2Te3 films, respectively. The planar devices basing on the geometrically designed high orientation films produce a remarkable temperature reduction of ~8.2 K in the hot spot elimination experiment, demonstrating the great benefit of Te assistant growth method for oriented planar Bi2Te3 films and planar devices devices design, and also bring great enlightenment to the next generation active thermal management for integrated circuits.

Thermoelectric performance of Cu3InSnSe5 and MnSe pseudo-binary solid solution

Cu3InSnSe5 is a newly discovered copper-based diamond-like thermoelectric semiconductor, whose thermoelectric performance can be further enhanced by the MnSe alloying herein. We observed the formation of MnSe2 precipitates that effectively scattered low-frequency phonons, which significantly reduced the lattice thermal conductivity at mid-to-low temperatures. While a high amount of MnSe alloying led to the formation of MnSe2 precipitates which enhanced the phonons scattering, a smaller MnSe content improved the power factor in a certain as well. Ultimately, our research achieved a peak ZT of 1.00 and an average ZT of 0.50 over the 300–773 K temperature range by 10 mol.% MnSe alloyed Cu3InSnSe5 pseudo-binary solid solution, demonstrating the potential of MnSe alloying for optimizing the thermoelectric performance of copper-based diamond-like semiconductor materials.

Enhanced Thermoelectric Properties of FeSe2 Alloys by Lattice Thermal Conductivity Reduction by Cl Doping

Enhanced Thermoelectric Properties of FeSe2 Alloys by Lattice Thermal Conductivity Reduction by Cl Doping

Chemical Pressure-Induced Unconventional Band Convergence Leads to High Thermoelectric Performance in SnTe.

Band convergence is considered a net benefit to thermoelectric performance as it decouples the density of states effective mass ( ) and carrier mobility (µ) by increasing valley degeneracy. Unlike conventional methods that typically prioritize at the expense of µ, this study theoretically demonstrates an unconventional band convergence strategy to enhance both and µ in SnTe under pressure. Density functional theory calculations reveal that increasing pressure from 0 to 5 GPa moves the Σ-band of SnTe upward, reducing the energy offset between L- and Σ-band from 0.35 to 0.2 eV while preserving the light band feature of the L-band. Consequently, a high power factor (PF) of 119.2 µW cm-1 K-2 at 300 K is achieved for p-type SnTe under 5 GPa. Chemical pressure also induces conduction band convergence, significantly enhancing the PF of n-type SnTe. Additionally, the interplay between pressure-induced phonon modes leads to a moderate increase in lattice thermal conductivity of SnTe below 3 GPa, which combined with the significantly enhanced PF, contributes to a large enhancement in ZT. Consequently, predicted ZT values of 2.12 at 650 K and 2.55 at 850 K are obtained for p- and n-type SnTe, respectively, showcasing substantial performance enhancements.

Thermoelectric properties of XX- and XY-stacked GeS/GeSe van der Waals heterostructures from DFT and BTP calculations.

This study utilizes density functional theory (DFT) and the Boltzmann transport equation (BTE) to investigate the structural, electronic, and thermoelectric properties of germanium sulfide (GeS) and germanium selenide (GeSe) monolayers, along with their van der Waals (vdW) heterostructures. We analyzed XX-stacked and XY-stacked configurations, where the XX configuration features direct atomic stacking, while the XY configuration exhibits staggered stacking. Our first-principles calculations indicate that the formation of GeS/GeSe heterostructures results in a reduction of bandgaps compared to their bulk and monolayer counterparts, yielding bandgap values of 0.91 eV for the XX configuration and 0.84 eV for the XY configuration. Stability assessments reveal that the XY configuration is more stable, demonstrating a lattice thermal conductivity of 15.21 W/mK compared to 17.95 W/mK for the XX configuration T 300 K. The thermoelectric properties were systematically evaluated across a temperature range of 300-800 K, revealing high Seebeck coefficients of 1.51 mV/K for the XX heterostructure and 1.39 mV/K for the XY heterostructure. reflecting their excellent charge transport capabilities. Notably, the figure of merit (ZT) at 800 K was calculated to be 0.90 for the XX configuration and 1.01 for the XY configuration, underscoring the superior thermoelectric performance of the XY heterostructure. These findings contribute to a comprehensive understanding of 2D GeS/GeSe heterostructures for thermoelectric applications and provide a solid foundation for future research and technological advancements in this domain.

Plasticity tuning of thermal conductivity between nanoparticles

We study the effects of uniaxial pressure on the thermal conductivity between two nanoparticles using atomistic simulation. While the system is compressed, we analyze the evolution of contact area, the relative density, and the dislocation density. Lattice thermal conductivity is calculated by non-equilibrium molecular dynamics simulations at several stages of the compression. Despite the increment of dislocation defects, thermal conductivity increases with pressure due to the increase in relative density and contact radius. The behavior of the contact radius is compared with the Johnson–Kendall–Roberts (JKR) model. While there is good agreement at low strain, after significant plasticity, signaled by the emission of dislocations from the contact region, the discrepancy with JKR grows larger with the dislocation density. The results for thermal conductivity show good agreement with previous studies at zero strain, and a theoretical model is used to accurately explain its behavior vs strain-dependent contact radius. Both the Kapitza resistance and thermal resistance decrease with strain but with very different evolution. Simulations of a bulk sample under uniaxial strain were also carried out, allowing for a clear distinction between the role of compressive stress, which increases the conductivity, vs the role of dislocations, which decrease the conductivity. For the NP system, there is the additional role of contact area, which increases with stress and also modifies conductivity. An analytical model with a single free parameter allows for a description of all these effects and matches both our bulk and NP simulation results.

Exploring the thermoelectric performance of NiFeMnAl and ZnFeVAl as novel quaternary Heusler compounds

Quaternary Heusler (QH) compounds, characterized by the chemical formula XX’YZ, are highly regarded in the energy materials sector due to their versatile electronic structures. The current study focuses on synthesizing novel QH compounds, NiFeMnAl and ZnFeVAl, through arc-melting followed by hot-pressing at 1073 K. Maximum Seebeck coefficients were exhibited ∼ −20.48 μV/K and ∼ −17.25 μV/K at 773 K for ZnFeVAl and NiFeMnAl, respectively. The evaluated power factor was ∼ 0.058 mWm−1K−2 for NiFeMnAl and ∼ 0.020 mWm−1K−2 for ZnFeVAl at 773 K. Furthermore, the lattice thermal conductivity (κl) was exhibited ∼ 8.73 Wm−1K−1 for NiFeMnAl and ∼ 6.92 Wm−1K−1 for ZnFeVAl at 773 K, with ZnFeVAl exhibiting a ∼ 20.73 % lower κl attributed to chemical bonding distortion arising from differences in constituent element electronegativity. Hence, these novel compounds offer a promising avenue for further research in TE materials, aiming to realize higher-performance materials for practical TE device applications.

Synergistic Suppression of Bipolar Effect and Lattice Thermal Conductivity Leading to High Average Figure of Merit in Bi0.4Sb1.6Te3 Materials through Alloying with AgSbTe2.

Bismuth telluride-based materials have been widely used in commercial thermoelectric applications due to their excellent thermoelectric performance in the near-room-temperature range, yet further improvement of their thermoelectric properties is still necessary. Moreover, the narrow band gap of these materials results in a bipolar effect at elevated temperatures, which causes severe degradation of the thermoelectric performance. In this work, the commercial Bi0.4Sb1.6Te3 was alloyed with AgSbTe2 by using high-energy ball milling method combined with spark plasma sintering. It was found that ball milling can effectively reduce the lattice thermal conductivity of the samples. The alloying of AgSbTe2 leads to a gradual increase in hole carrier concentration, resulting in an enhanced electrical conductivity and optimized power factor. Additionally, the bipolar effect is also weakened due to the increased hole carrier concentration. Furthermore, the substitution of Ag in the Bi/Sb sublattice causes further reduction in the lattice thermal conductivity. Ultimately, the sample alloyed with 0.15 wt % AgSbTe2 demonstrates its best thermoelectric performance with a maximum zT of 1.35 at 393 K, showing a 20.5% improvement compared to the commercial sample. Besides, its average zT reaches a high value of 1.25 between 303 and 483 K, with a 27.6% improvement compared to that of the commercial sample.

Pressure-regulated rotational guests in nano-confined spaces suppress heat transport in methane hydrates

Materials with low lattice thermal conductivity are essential for various heat-related applications like thermoelectrics, and usual approaches for achieving this rely on specific crystalline structures. Here, we report a strategy for thermal conductivity reduction and regulation via guest rotational dynamics and their couplings with lattice vibrations. By applying pressure to manipulate rotational states, we find the intensified rotor-lattice couplings of compressed methane hydrate MH-III can trigger strong phonon scatterings and phonon localizations, enabling an almost three-fold suppression of thermal conductivity. Besides, the disorder in methane rotational dynamics results in anharmonic interactions and nonlinear pressure-dependent heat transport. The overall guest rotational dynamics and heat conduction changes can be flexibly regulated by the rotor-lattice coupling strength. We further underscore that this reduction mechanism can be extended to a wide range of systems with different structures. The results demonstrate a potentially universal method for reducing or controlling heat transport by developing a hybrid system with tailored molecular rotors.

Machine Learning and First-Principle Predictions of Materials with Low Lattice Thermal Conductivity.

We performed machine learning (ML) simulations and density functional theory (DFT) calculations to search for materials with low lattice thermal conductivity, κL. Several cadmium (Cd) compounds containing elements from the alkali metal and carbon groups including A2CdX (A = Li, Na, and K; X = Pb, Sn, and Ge) are predicted by our ML models to exhibit very low κL values (<1.0 W/mK), rendering these materials suitable for potential thermal management and insulation applications. Further DFT calculations of electronic and transport properties indicate that the figure of merit, ZT, for the thermoelectric performance can exceed 1.0 in compounds such as K2CdPb, K2CdSn, and K2CdGe, which are therefore also promising thermoelectric materials.

Low Lattice Thermal Conductivity and Anisotropic Thermal Transport Properties of the Layered BiAgOTe Material in Consideration of Four-Phonon Scattering: A First-Principles Investigation

Low Lattice Thermal Conductivity and Anisotropic Thermal Transport Properties of the Layered BiAgOTe Material in Consideration of Four-Phonon Scattering: A First-Principles Investigation

Achieving low thermal conductivity and high quality factor in sextuple-doped TiS2

Transition-metal dichalcogenide TiS2 stands out as a sustainable candidate for room- and medium-temperature thermoelectric materials due to its affordability, non-toxicity, eco-friendly nature and use of non-critical elements. However, its light element compositional nature results in a large thermal conductivity, which is the main limitation of the thermoelectric performance of TiS2. Here, we report a multi-element doping strategy by incorporating equivalent (Se, Zr) elements and introducing higher-valence (Nb, Ta) and lower-valence (Y, La) elements in pairs to minimize its lattice thermal conductivity, κlat. The findings indicate a nearly 50% decrease in κlat across the entire temperature range, attributed to the presence of strong point-defect scattering after multi-element doping. Additionally, we observed a reduced dependency of κlat on temperature in multi-element doped TiS2, as point defects can effectively scatter phonons at room temperature. As a result, the multi-element doped TiS2 attained its highest ZT value of approximately 0.4 at 625 K. Incorporating higher-valence and lower-valence elements in pairs proves to be an effective method for decreasing lattice thermal conductivity without compromising too much of its large Seebeck coefficient.