Room Temperature Lattice Thermal Conductivity Research Articles

Janus-like Structure and Resonance Level Actualized Ultralow Lattice Thermal Conductivity and Enhanced ZTave in Mg3(Sb, Bi)2-Based Zintls.

Grain boundary (GB) engineering includes grain size and GB segregation. Grain size has been proven to affect the electrical properties of Mg3(Sb, Bi)2 at low temperatures. However, the formation mechanism of GB segregation and what kind of GB segregation is beneficial to the performance are still unclear. Here, the Ga/Bi cosegregation at GBs and Mg segregation within grains optimize the transport of electrons and phonons simultaneously. Ga/Bi cosegregation promotes the formation of Janus-like structures due to the diverse ordering tendencies of liquid Mg3Sb2 and Mg3Bi2 and the absence of a solid solution of Ga/Bi. The Janus-like structure significantly reduces the room-temperature lattice thermal conductivity by introducing diverse microdefects. Meanwhile, a coherent interface between the nano Mg segregation region and the matrix is formed, which reduces the thermal conductivity without affecting the carrier transport. Furthermore, the band structure calculations show that Ga doping introduces the resonance level, increasing the Seebeck coefficient. Finally, the lattice thermal conductivity reaches ∼0.4 W m-1 K-1, and a high average ZT of 1.21 between 323 and ∼773 K is achieved for Mg3.2Y0.02Ga0.03Sb1.5Bi0.5. This work provides guidance for improving the thermoelectric performance via designing cosegregation.

Ultralow lattice thermal conductivity in type-I Dirac MBene TiB2

MBenes, the emergent novel two-dimensional family of transition metal borides have recently attracted remarkable attention. Transport studies of such two-dimensional structures are very rare and are of sparking interest. In this paper Using Boltzmann transport theory with ab-initio inputs from density functional theory, we examined the transport in TiB2 MBene system, which is highly dependent on number of layers. We have shown that the addition of an extra layer (as in bilayer BL) destroys the formation of type-I Dirac state by introducing the positional change and tilt to the Dirac cones, thereby imparting the type-II Weyl metallic character in contrast to Dirac-semimetallic character in monolayer ML. Such non-trivial electronic ordering significantly impacts the transport behavior. We further show that the anisotropic room temperature lattice thermal conductivity κ L for ML (BL) is observed to be 0.41 (0.52) and 2.00 (2.04) W m−1 K−1 for x and y directions, respectively, while the high temperature κ L (ML 0.13 W m−1 K−1 and BL 0.21 W m−1 K−1 at 900 K in x direction) achieves ultralow values. Our analysis reveals that such values are attributed to enhanced anharmonic phonon scattering, enhanced weighted phase space and co-existence of electronic and phononic Dirac states. We have further calculated the electronic transport coefficients for TiB2 MBene, where the layer dependent competing behavior is observed at lower temperatures. Our results further unravels the layer dependent thermoelectric performance, where ML is shown to have promising room-temperature thermoelectric figure of merit (ZT) as 1.71 compared to 0.38 for BL.

Can Pressure be a Good Strategy for Optimizing Thermoelectric Performance of SnPS3${\rm SnPS}_3$?

AbstractExternal pressure can significantly alter the transport coefficients, power factor, and figure of merit because of its direct influence on the electronic structure, electron–phonon, and phonon–phonon couplings. This study delves into the electronic and thermal transport properties of at external pressures up to 30 GPa using first‐principles calculations and Boltzmann transport theory. The electron–phonon relaxation time is computed within the electron–phonon‐averaged (EPA) approximation, enabling exploration beyond the constant relaxation time approximation. The first‐principles calculations reveal an indirect bandgap of 1.76 (without pressure) and 0.12 eV (30 GPa). The density functional perturbation theory calculations confirm the dynamic stability of at external pressure up to 30 GPa. The electronic transport properties are improved by more than one order of magnitude at 30 GPa, consistent with experimental observations. The Peierls–Boltzmann transport calculations demonstrate the room temperature lattice thermal conductivity of 0.22 (without pressure) and 7.4 (at 30 GPa). The results emanate that exhibits of 0.71 at 900 K at a hole doping of 2 at zero pressure, which decreases with increasing pressure. The findings explore the effect of external pressure on both electronic and thermal transport properties of , warranting further experimental exploration of thermal transport properties at higher pressures.

Room Temperature Lattice Thermal Conductivity of GeSn Alloys.

CMOS-compatible materials for efficient energy harvesters at temperatures characteristic for on-chip operation and body temperature are the key ingredients for sustainable green computing and ultralow power Internet of Things applications. In this context, the lattice thermal conductivity (κ) of new group IV semiconductors, namely Ge1-xSnx alloys, are investigated. Layers featuring Sn contents up to 14 at.% are epitaxially grown by state-of-the-art chemical-vapor deposition on Ge buffered Si wafers. An abrupt decrease of the lattice thermal conductivity (κ) from 55 W/(m·K) for Ge to 4 W/(m·K) for Ge0.88Sn0.12 alloys is measured electrically by the differential 3ω-method. The thermal conductivity was verified to be independent of the layer thickness for strained relaxed alloys and confirms the Sn dependence observed by optical methods previously. The experimental κ values in conjunction with numerical estimations of the charge transport properties, able to capture the complex physics of this quasi-direct bandgap material system, are used to evaluate the thermoelectric figure of merit ZT for n- and p-type GeSn epitaxial layers. The results highlight the high potential of single-crystal GeSn alloys to achieve similar energy harvest capability as already present in SiGe alloys but in the 20 °C-100 °C temperature range where Si-compatible semiconductors are not available. This opens the possibility of monolithically integrated thermoelectric on the CMOS platform.

Improvement of the Thermoelectric Properties of p-Type Mg3Sb2 by Mg-Site Double Substitution.

A P-type Mg3Sb2-based Zintl phase compound has been considered a promising candidate for thermoelectric applications. Alloying, which introduces a high concentration of point defects, is particularly effective in scattering phonons and reducing lattice thermal conductivity. Herein, alloying in p-type Mg2.995Na0.005Sb2 via the introduction of elements like Yb, Eu, Ca, and Ba was realized, and the room-temperature lattice thermal conductivity has been effectively reduced to ∼1.1 W m-1 K-1. To further intensify the phonon scattering, two groups of elements (Eu and Cd, and Yb and Cd) were chosen for heavy alloying at the Mg site, and the lattice thermal conductivity of Mg1.49Eu0.5Cd1Na0.01Sb2 was further reduced to ∼0.45 W m-1 K-1. Eventually, a peak zT as high as ∼1.0 was achieved at 773 K, and the compound outperforms the previously reported p-type Mg3Sb2 compounds.

Implications and Optimization of Domain Structures in IV-VI High-Entropy Thermoelectric Materials.

High-entropy semiconductors are now an important class of materials widely investigated for thermoelectric applications. Understanding the impact of chemical and structural heterogeneity on transport properties in these compositionally complex systems is essential for thermoelectric design. In this work, we uncover the polar domain structures in the high-entropy PbGeSnSe1.5Te1.5 system and assess their impact on thermoelectric properties. We found that polar domains induced by crystal symmetry breaking give rise to well-structured alternating strain fields. These fields effectively disrupt phonon propagation and suppress the thermal conductivity. We demonstrate that the polar domain structures can be modulated by tuning crystal symmetry through entropy engineering in PbGeSnAgxSbxSe1.5+xTe1.5+x. Incremental increases in the entropy enhance the crystal symmetry of the system, which suppresses domain formation and loses its efficacy in suppressing phonon propagation. As a result, the room-temperature lattice thermal conductivity increases from κL = 0.63 Wm-1 K-1 (x = 0) to 0.79 Wm-1 K-1 (x = 0.10). In the meantime, the increase in crystal symmetry, however, leads to enhanced valley degeneracy and improves the weighted mobility from μw = 29.6 cm2 V-1 s-1 (x = 0) to 35.8 cm2 V-1 s-1 (x = 0.10). As such, optimal thermoelectric performance can be achieved through entropy engineering by balancing weighted mobility and lattice thermal conductivity. This work, for the first time, studies the impact of polar domain structures on thermoelectric properties, and the developed understanding of the intricate interplay between crystal symmetry, polar domains, and transport properties, along with the impact of entropy control, provides valuable insights into designing GeTe-based high-entropy thermoelectrics.

Origin of low lattice thermal conductivity in promising ternary PbmBi2S3+m (m = 1–10) thermoelectric materials

Ternary Pb-Bi-S compounds emerge as potential thermoelectric materials owing to low thermal conductivity, but the origin of their intrinsic low lattice thermal conductivities lacks further investigation. Herein, a series of ternary PbmBi2S3+m (m = 1–10) compounds are synthesized and their crystal structure evolutions with increasing m values are clearly unclosed. The room-temperature lattice thermal conductivities in PbBi2S4, Pb3Bi2S6 and Pb6Bi2S9 can reach at 0.57, 0.56 and 0.80 W m−1 K−1, respectively, outperforming other ternary sulfur-based compounds. Theoretical calculations show that the low lattice thermal conductivities in PbmBi2S3+m (m = 1–10) mainly originate from soft phonon dispersion caused by strong lattice anharmonicity, and both asymmetric chemical bond and lone pair electrons (Pb 6s2 and Bi 6s2) can favorably block phonon propagation. Furthermore, the elastic measurements also confirm relatively low sound velocities and shear modulus, and the Grüneisen parameter (γ) calculated by sound velocities can reach at 1.67, 1.85 and 1.94 in PbBi2S4, Pb3Bi2S6 and Pb6Bi2S9, respectively. Finally, the intrinsic low lattice thermal conductivities in PbmBi2S3+m (m = 1–10) contribute to promising thermoelectric performance, and the maximum ZT values of 0.47, 0.38 and 0.45 can be achieved in undoped PbBi2S4, Pb3Bi2S6 and Pb6Bi2S9, respectively.

Phonon stability boundary and deep elastic strain engineering of lattice thermal conductivity

Recent studies have reported the experimental discovery that nanoscale specimens of even a natural material, such as diamond, can be deformed elastically to as much as 10% tensile elastic strain at room temperature without the onset of permanent damage or fracture. Computational work combining ab initio calculations and machine learning (ML) algorithms has further demonstrated that the bandgap of diamond can be altered significantly purely by reversible elastic straining. These findings open up unprecedented possibilities for designing materials and devices with extreme physical properties and performance characteristics for a variety of technological applications. However, a general scientific framework to guide the design of engineering materials through such elastic strain engineering (ESE) has not yet been developed. By combining first-principles calculations with ML, we present here a general approach to map out the entire phonon stability boundary in six-dimensional strain space, which can guide the ESE of a material without phase transitions. We focus on ESE of vibrational properties, including harmonic phonon dispersions, nonlinear phonon scattering, and thermal conductivity. While the framework presented here can be applied to any material, we show as an example demonstration that the room-temperature lattice thermal conductivity of diamond can be increased by more than 100% or reduced by more than 95% purely by ESE, without triggering phonon instabilities. Such a framework opens the door for tailoring of thermal-barrier, thermoelectric, and electro-optical properties of materials and devices through the purposeful design of homogeneous or inhomogeneous strains.

N-Type Thermoelectric AgBiPbS3 with Nanoprecipitates and Low Thermal Conductivity.

Thermoelectric sulfide materials are of particular interest due to the earth-abundant and cost-effective nature of sulfur. Here, we report a new n-type degenerate semiconductor sulfide, AgBiPbS3, which adopts a Fm3̅m structure with a narrow band gap of ∼0.32 eV. Despite the homogeneous distribution of elements at the scale of micrometer, Ag2S nanoprecipitates with dimensions of several nanometers were detected throughout the matrix. AgBiPbS3 exhibits a low room-temperature lattice thermal conductivity of 0.88 W m-1 K-1, owing to the intrinsic low lattice thermal conductivity of Ag2S and the effective scattering of phonons at nanoprecipitate boundaries. Moreover, compared to AgBiS2, AgBiPbS3 demonstrates a significantly improved weighted mobility of >16 cm2 V-1 s-1 at 300 K, leading to an enhanced PF of 1.6 μW cm-1 K-2 at 300 K. The superior electrical transport in AgBiPbS3 can be attributed to the high valley degeneracy of the L point (the conduction band minimum), which is contributed by the Pb s and Pb p orbitals. Further, Ga doping is found to be effective in modulating the Fermi levels of AgBiPbS3, leading to further enhancement of PF with a PFave of 2.7 μW cm-1 K-2 in the temperature range of 300-823 K. Consequently, a relatively high ZTave of 0.22 and a peak ZT of ∼0.4 at 823 K have been achieved in 3% Ga-doped AgBiPbS3, highlighting the potential of AgBiPbS3 as an n-type thermoelectric sulfide.

Electronic, Thermal and Mechanical Properties of Carbon and Boron Nitride Holey Graphyne Monolayers.

In a recent experimental accomplishment, a two-dimensional holey graphyne semiconducting nanosheet with unusual annulative π-extension has been fabricated. Motivated by the aforementioned advance, herein we theoretically explore the electronic, dynamical stability, thermal and mechanical properties of carbon (C) and boron nitride (BN) holey graphyne (HGY) monolayers. Density functional theory (DFT) results reveal that while the C-HGY monolayer shows an appealing direct gap of 1.00 (0.50) eV according to the HSE06(PBE) functional, the BNHGY monolayer is an indirect insulator with large band gaps of 5.58 (4.20) eV. Furthermore, the elastic modulus (ultimate tensile strength) values of the single-layer C- and BN-HGY are predicted to be 127(41) and 105(29) GPa, respectively. The phononic and thermal properties are further investigated using machine learning interatomic potentials (MLIPs). The predicted phonon spectra confirm the dynamical stability of these novel nanoporous lattices. The room temperature lattice thermal conductivity of the considered monolayers is estimated to be very close, around 14.0 ± 1.5 W/mK. At room temperature, the C-HGY and BN-HGY monolayers are predicted to yield an ultrahigh negative thermal expansion coefficient, by more than one order of magnitude larger than that of the graphene. The presented results reveal decent stability, anomalously low elastic modulus to tensile strength ratio, ultrahigh negative thermal expansion coefficients and moderate lattice thermal conductivity of the semiconducting C-HGY and insulating BN-HGY monolayers.

Enhanced thermoelectric performance of n-type PbTe through introducing PbSe by a fast preparation method

N-type PbTe-based materials exhibit promising thermoelectric performance around 600–900 K, while the near room-temperature thermoelectric performance still needs to be improved due to their high thermal conductivity. Forming solid solutions is an effective strategy to strengthen phonon scatterings and results in lower lattice thermal conductivity. However, the existing preparation methods used in PbTe-based solid solutions are time-consuming and energy-intensive, which limits their further applications. Herein, we report a fast method combined self-propagating high-temperature synthesis (SHS) with spark plasma sintering (SPS) to successfully fabricate PbTe–PbSe solid solutions. Due to the mass and strain fluctuations, a largely reduced room temperature lattice thermal conductivity of 1.27 W m−1 K−1 was achieved in (Pb0.995Bi0.005Te)0.8-(PbSe)0.2, which was 40% lower than that of pristine Pb0.995Bi0.005Te. Besides, carrier mobility increased after PbSe alloying, leading to comparable electrical performance. Consequently, a maximum average thermoelectric figure of merit ZTave reached 0.57 at 300–623 K of (Pb0.995Bi0.005Te)0.8-(PbSe)0.2 and was 21% and 24% higher than those of pristine Pb0.995Bi0.005Te and PbSe, respectively. Such a simple and effective method is expected to be further adopted in other thermoelectric solid solutions.

Hexagonal boron-carbon fullerene heterostructures; Stable two-dimensional semiconductors with remarkable stiffness, low thermal conductivity and flat bands

Among exciting recent advances in the field of two-dimensional (2D) materials, the successful fabrications of the C60 fullerene networks has been a particularly inspiring accomplishment. Motivated by the recent achievements, herein we explore the stability and physical properties of novel hexagonal boron-carbon fullerene 2D heterostructures, on the basis of already synthesized B40 and C36 fullerenes. By performing extensive structural minimizations of diverse atomic configurations using the density functional theory method, for the first time, we could successfully detect thermally and dynamically stable boron-carbon fullerene 2D heterostructures. Density functional theory results confirm that the herein predicted 2D networks exhibit very identical semiconducting electronic natures with topological flat bands. Using the machine learning interatomic potentials, we also investigated the mechanical and thermal transport properties. Despite of different bonding architectures, the room temperature lattice thermal conductivity of the predicted nanoporous fullerene heterostructures was found to range between 4 and 10 W/mK. Boron-carbon fullerene heterostructures are predicted to show anisotropic but also remarkable mechanical properties, with tensile strengths and elastic modulus over 8 and 70 GPa, respectively. This study introduces the possibility of developing a novel class of 2D heterostructures based on the fullerene cages, with attractive electronic, thermal and mechanical features.

Structural, electronic, thermal and mechanical properties of C60-based fullerene two-dimensional networks explored by first-principles and machine learning

Recent experimental reports on the realizations of two-dimensional (2D) networks of the C60-based fullerenes with anisotropic and nanoporous lattices represent a significant advance, and create exciting prospects for the development of a new class of nanomaterials. In this work, we employed theoretical calculations to explore novel C60-based fullerene lattices and subsequently evaluate their stability and key physical properties. After the energy minimization of extensive structures, we could detect novel 2D, 1D and porous carbon C60-based networks, with close energies to that of the isolated C60 cage. Density functional theory results confirm that the C60-based networks can exhibit remarkable thermal stability, and depending on their atomic structure show metallic, semimetallic or semiconducting electronic nature. Using the machine learning interatomic potentials, thermal and mechanical responses of the predicted nanoporous 2D lattices were investigated. The estimated thermal conductivity of the quasi-hexagonal-phase of C60 fullerene is shown to be in an excellent agreement with the experimental measurements. Despite of different atomic structures, the anisotropic room temperature lattice thermal conductivity of the fullerene nanosheets are estimated to be in the order of 10 W/mK. Unlike the majority of carbon-based 2D materials, C60-based counterparts noticeably are predicted to show positive thermal expansion coefficients. Porous carbon C60-based networks are found to exhibit superior mechanical properties, with tensile strengths and elastic modulus reaching extraordinary values of 50 and 300 GPa, respectively. The theoretical results presented in this work provide a comprehensive vision on the structural, energetic, electronic, thermal and mechanical properties of the C60-based fullerene networks.

Colossal figure of merit and compelling HER catalytic activity of holey graphyne

Herein, we have conducted a comprehensive study to uncover the thermal transport properties and hydrogen evolution reaction catalytic activity of recently synthesized holey graphyne. Our findings disclose that holey graphyne has a direct bandgap of 1.00 eV using the HSE06 exchange–correlation functional. The absence of imaginary phonon frequencies in the phonon dispersion ensures its dynamic stability. The formation energy of holey graphyne turns out to be − 8.46 eV/atom, comparable to graphene (− 9.22 eV/atom) and h-BN (− 8.80 eV/atom). At 300 K, the Seebeck coefficient is as high as 700 μV/K at a carrier concentration of 1 × 1010 cm-2. The predicted room temperature lattice thermal conductivity (κl) of 29.3 W/mK is substantially lower than graphene (3000 W/mK) and fourfold smaller than C3N (128 W/mK). At around 335 nm thickness, the room temperature κl suppresses by 25%. The calculated p-type figure of merit (ZT) reaches a maximum of 1.50 at 300 K, higher than that of holey graphene (ZT = 1.13), γ-graphyne (ZT = 0.48), and pristine graphene (ZT = 0.55 × 10–3). It further scales up to 3.36 at 600 K. Such colossal ZT values make holey graphyne an appealing p-type thermoelectric material. Besides that, holey graphyne is a potential HER catalyst with a low overpotential of 0.20 eV, which further reduces to 0.03 eV at 2% compressive strain.

Atomistic Insights into the Origin of High-Performance Thermoelectric Response in Hybrid Perovskites.

Due to their tantalizing prospect of heat-electricity interconversion, hybrid organic-inorganic perovskites have sparked considerable research interests recently. Nevertheless, understanding their complex interplay between the macroscopic properties, nonintuitive transport processes, and basic chemical structures still remains far from completion, although it plays a fundamental role in systematic materials development. On the basis of multiscale first-principles calculations, this understanding is herein advanced by establishing a comprehensive picture consisting of atomic and charge dynamics. It is unveiled that the ultralow room-temperature lattice thermal conductivity (≈0.20W m-1 K-1 ) of hybrid perovskites is critical to their decent thermoelectric figure of merit (≈0.34), and such phonon-glass behavior stems from not only the inherent softness but also the strong anharmonicity. It is identified that the 3D electrostatic interaction and hydrogen-bonded networks between the PbI3- cage and embedded cations result in the strongly coupled motions of inorganic framework and cation, giving rise to their high degree of anharmonicity. Furthermore, such coupled motions bring about low-frequency optical vibrational modes, which leads to the dominant role of electron scattering with optical phonons in charge transport. It is expected that these new atomistic-level insights offer a standing point where the performance of thermoelectric perovskites can be further enhanced.

Microstructural Manipulation for Enhanced Average Thermoelectric Performance: A Case Study of Tin Telluride

Achieving a high average figure of merit in a low-cost/toxic compound, tin telluride (SnTe), is crucial for thermoelectric applications. Introducing gap-like structures into the rock–salt matrix once elucidated a large potential; however, the poor quantity and controllability of the planar defects become the drawbacks. Here, we demonstrate, by electron microscopy and X-ray diffraction, that dense planar cationic vacancies can be produced in Sb2Te3(Sn1–xGexTe)8 samples for the first time, leading to an effective targeted solution. On the basis of the optimized lattice matrix, a low room-temperature lattice thermal conductivity of ∼0.7 W m–1 K–1 (25% of pristine SnTe) can be achieved. Additionally, the first-principles calculation result reveals that the value of density-of-state effective mass is increased after manipulating the local cation matrix, resulting in an outstanding power factor of ∼2.5 mW m–1 K–2 at 723 K when x = 0.2. Eventually, a competitive maximum figure of merit ZTmax of ∼1.3 at 723 K and an excellent average ZT value of ∼0.78 at 323–773 K are simultaneously realized in Sb2Te3(Sn0.8Ge0.2Te)8. This pioneered study about manipulating gap-like structures and its effects on the transport properties of SnTe-based materials would also provide a promising alternative for pursuing other high ZTave compounds in the future.

Understanding the origins of low lattice thermal conductivity in a novel two-dimensional monolayer NaCuS for achieving medium-temperature thermoelectric applications

Understanding the lattice dynamics from the perspective of chemical bonds and phonon transport is essential for finding and designing high-efficiency thermoelectric (TE) materials and achieving applications. The coexistence of weak chemical bonding and strong phonon anharmonicity is elucidated as the origin of the intrinsically low lattice thermal conductivity by combining the first principles with the Boltzmann transport theory. By utilizing the crystal orbital Hamilton population (COHP) analysis, the weaker Cu-S chemical bonding originating from the filled antibonding orbitals gives rise to the low average phonon group velocity (va). Here, this research also investigates the scattering processes (the out-of-plan acoustic mode (ZA) + optical mode (O) → O (ZA + O → O), the in-plane transverse acoustic mode (TA) + O → O (TA + O → O), and the in-plane longitudinal acoustic mode (LA) + O → O (LA + O → O)), from which we find that 2D NaCuS possesses strong phonon anharmonicity. The low va and strong phonon scattering enable 2D NaCuS to exhibit a low room temperature lattice thermal conductivity (klat) of 1.95 W/mK. Furthermore, our studies demonstrate 2D NaCuS presents a high ZT of 1.44 at 500 K due to the low klat and excellent electronic transport performance. This study demonstrates that 2D NaCuS is identified as a new TE material for promising medium-temperature applications.

Antibonding p-d and s-p Hybridization Induce the Optimization of Thermal and Thermoelectric Performance of MGeTe3 (M = In and Sb)

Manipulation of phonon transport is the key to optimizing the overall energy conversion efficiency of thermoelectric materials. In this work, we demonstrate that the antibonding hybridization resulting from elemental substitution can weaken the interatomic interactions, which in turn enhances the structural anharmonicity and hinders the heat conduction of layered ABTe3 (ABSe3) (A = Al, Ga, In, As, and Sb; B = Si and Ge) compounds. It is revealed that the filled antibonded p-d state of GaSiTe3 (GaSiSe3) originates from the mixture of Ga-3d and Te-5p (Se-4p) orbitals, whereas the outer As-s electrons hybridize with the Te (Se)-p electrons to form antibonding states in AsSiTe3 (AsSiSe3). Consequently, the room temperature lattice thermal conductivity (κL) of AlGeTe3 (AlGeSe3) is reduced from 3.27 (3.86) W/mK to 0.62 (1.47) W/mK for GaSiTe3 (GaSiSe3) and 1.91 (1.74) W/mK for AsSiTe3 (AsSiSe3) in spite of their similar atomic masses and crystal structures. Based on these findings, we propose candidates of InGeTe3 and SbGeTe3 to realize potentially high thermoelectric performance by rationally incorporating heavy weight elements but still maintaining weak atomic binding interactions. Due to the low κL of 0.26 (0.6) W/mK, a high n-type (p-type) ZT value of 2.18 (1.08) at 750 (650) K is finally captured in InGeTe3 (SbGeTe3). Our results not only provide insights to understand the relationship between chemical bonding and lattice thermal conductivity but also offer an approach to design and discover materials with expected thermal transport and thermoelectric properties.

Giant phonon anomaly in topological nodal-line semimetals

The band topology has been revealed to bring a wide array of novel electronic transport phenomena, but its interaction with phonon properties remains largely unexplored. Here we propose that continuous topological singularities with variable Fermi wave vectors can lead to giant effects on phonon transport in nodal-line semimetals. Using first-principles calculations, we show that such an exotic feature is present in a well-known topological semimetal ZrSiSe, in which the unique nodal-line can guarantee considerable momentum-continuous phonons to satisfy the stringent condition of Kohn anomaly and thereby dramatically strengthen the electron-phonon coupling. Moreover, the momentum-continuous anomaly phonons with eight arms of vertical Fermi surface drive intense phonon-electron scattering that is even comparable with intrinsic phonon-phonon scattering, giving rise to a reduction of ∼45% on room temperature lattice thermal conductivity. Our findings not only uncover giant phonon anomaly in topological nodal-line semimetals but also provide guidance for exploring the vital influence of electronic band topology on thermal transport bridged by the electron-phonon coupling.

Enhanced Thermoelectric Efficiency through Li-Induced Phonon Softening in CuGaTe2

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.