Lattice Thermal Transport Research Articles

Lone Pair Induced 1D Character and Weak Cation-Anion Interactions: Two Ingredients for Low Thermal Conductivity in Mixed-Anion Metal Chalcohalide CuBiSCl2.

Mixed-anion compounds, which incorporate multiple types of anions into materials, display tailored crystal structures and physical/chemical properties, garnering immense interest in various applications such as batteries, catalysis, photovoltaics, and thermoelectrics. However, detailed studies regarding correlations among crystal structure, chemical bonding, and thermal/vibrational properties are rare for these compounds, which limits the exploration of mixed-anion compounds for associated thermal applications. In this work, we investigate the lattice dynamics and thermal transport properties of the metal chalcohalide, CuBiSCl2. A high-purity polycrystalline CuBiSCl2 sample exhibits a low lattice thermal conductivity (κL) of 0.9-0.6 W/(m·K) from 300 to 573 K. By combining various experimental techniques, including three-dimensional (3D) electron diffraction, with theoretical calculations, we elucidate the origin of low κL in CuBiSCl2. The stereochemical activity of the 6s2 lone pair of Bi3+ favors an asymmetric environment with neighboring anions involving both short and long bond lengths. This particularity often implies weak bonding, low structure dimensionality, and strong anharmonicity, leading to a low κL. In addition, the strong 2-fold linear S-Cu-S coordination with weak Cu···Cl interactions induces a large anisotropic vibration of Cu, which enables strong phonon-phonon scattering and decreases κL. The investigations into lattice dynamics and thermal transport properties of CuBiSCl2 broaden the scope of the existing mixed-anion compounds suitable for the associated thermal applications, offering a new avenue for the search for low thermal conductivity materials in low-cost mixed-anion compounds.

Lattice thermal conductivity and phonon transport properties of monolayer fluorographene

Lattice thermal conductivity and phonon transport properties of monolayer fluorographene

Influence of quartic anharmonicity on lattice dynamics and thermal transport properties of 16 antifluorite structures

Influence of quartic anharmonicity on lattice dynamics and thermal transport properties of 16 antifluorite structures

Disorder-dominated and scattering-dominated thermal transport in clathrate hydrates

Methane hydrate (MH) is an ice-like compound where methane molecules are encased within a lattice of water molecules. Found abundantly on ocean floors, MHs can influence future methane supplies, ocean floor stability, and climate change. In this study, a high-precision deep neural network interatomic potential for MHs is developed using ab initio molecular dynamics. Our findings reveal a transition between disorder-dominated and scattering-dominated lattice thermal transport in partially filled MHs, which are the most common form in real-world conditions. Although guest methane molecules have a minimal effect on the anharmonicity of the host lattice and the phonon band structure, they significantly increase the scattering rate of host lattice phonons by enlarging their anharmonic scattering phase space. Spectral phonon analysis further shows that methane guest molecules scatter low-frequency phonons associated with water molecule vibrations, considerably reducing the thermal conductivity of filled MHs.

Lattice dynamic and anomalous thermal transport of calcium sodium vanadates

Calcium sodium vanadate compounds, including NaCaVO4 and Na2CaV4O12, have garnered significant interest for their extensive potential in various practical applications. Nonetheless, a comprehensive understanding of their intrinsic thermophysical properties remains elusive. Here, we present a comprehensive theoretical study on the lattice dynamic, thermodynamic properties, and thermal transport of NaCaVO4 and Na2CaV4O12. The thermodynamic properties including the heat capacity, thermal expansion coefficient, and Gibbs free energy over a wide range of temperatures are obtained. Moreover, utilizing the unified theory, we reveal the hierarchical thermal transport properties of NaCaVO4 and Na2CaV4O12, with diffusive channels making a significant contribution to the lattice thermal conductivity (κL). This contributes to the weak temperature dependence of κL, deviating from the typical κL ∼T-1 trend. With the consideration of normal and diffusive phonons, we predict the ultralow thermal conductivities of NaCaVO4 and Na2CaV4O12, which is derived from the bonding heterogeneity with the coexistence of weak Na-O (Ca-O) bonds and strong V-O bonds. This work offers crucial insights into the lattice dynamics and thermophysical characteristics of metal layered vanadates, potentially enhancing the utility of calcium sodium vanadate in various technological implementations.

Effects of Rattling Behavior of K and Cd Atoms along Different Directions in Anisotropic KCdAs on Lattice Thermal Transport and Thermoelectric Properties

We employ advanced first principles methodology, merging self‐consistent phonon theory and the Boltzmann transport equation, to comprehensively explore the thermal transport and thermoelectric properties of KCdAs. Notably, the study accounts for the impact of quartic anharmonicity on phonon group velocities in the pursuit of lattice thermal conductivity and investigates 3ph and 4ph scattering processes on phonon lifetimes. Through various methodologies, including examining atomic vibrational modes and analyzing 3ph and 4ph scattering processes, the article unveils microphysical mechanisms contributing to the low κL within KCdAs. Key features include significant anisotropy in Cd atoms, pronounced anharmonicity in K atoms, and relative vibrations in non‐equivalent As atomic layers. Cd atoms, situated between As layers, exhibit rattling modes and strong lattice anharmonicity, contributing to the observed low κL. Remarkably flat bands near the valence band maximum translate into high PF, aligning with ultralow κL for exceptional thermoelectric performance. Under optimal temperature and carrier concentration doping, outstanding ZT values are achieved: 4.25 (a(b)‐axis, p‐type, 3 × 1019 cm−3, 500 K), 0.90 (c‐axis, p‐type, 5 × 1020 cm−3, 700 K), 1.61 (a(b)‐axis, n‐type, 2 × 1018 cm−3, 700 K), and 3.06 (c‐axis, n‐type, 9 × 1017 cm−3, 700 K).

Strong electron-phonon coupling and high lattice thermal conductivity in half-Heusler thermoelectric materials.

Traditional half-Heusler thermoelectric materials, identified as 18-electron compounds, are characterized by the high power factor and the high lattice thermal conductivity. Interestingly, the emerging 19-electron half-Heusler compounds were also found to be promising thermoelectric materials, but with a 5-10 times lower lattice thermal conductivity. Since the two kinds of compounds have similar chemical and physical structures, such as TiCoSb and VCoSb, the large difference in lattice thermal conductivity is a puzzling question. Here, we present a theoretical study to clarify the lattice thermal transport in half-Heusler thermoelectric materials. Based on electronic band structure analysis, we show that the two transition-metal elements in half-Heusler compounds form the strong and direct d-d interaction that is responsible for the high lattice thermal conductivity of 18-electron compounds. In 19-electron half-Heusler compounds, however, the extra valence electron enters the d-d antibonding states, which significantly weakens the atomic bond strength, leading to a large decrease in the cohesive energy. The resulting softened acoustic phonons enhance the phonon-phonon scattering, and thus reduce the lattice thermal conductivity significantly. By constructing an artificial 18-e compound V0.5Sc0.5CoSb, it is proved that the one less electron relative to VCoSb increases the lattice thermal conductivity significantly.

Unravelling ultralow thermal conductivity in perovskite Cs2AgBiBr6: dominant wave-like phonon tunnelling and strong anharmonicity

Understanding the lattice dynamics and heat transport physics in the lead-free halide double perovskites remains an outstanding challenge due to their lattice dynamical instability and strong anharmonicity. In this work, we investigate the microscopic mechanisms of anharmonic lattice dynamics and thermal transport in lead-free halide double perovskite Cs2AgBiBr6 from first principles. We combine self-consistent phonon calculations with bubble diagram correction and a unified theory of lattice thermal transport that considers both the particle-like phonon propagation and wave-like tunnelling of phonons. An ultra-low thermal conductivity at room temperature (~0.21 Wm−1K−1) is predicted with weak temperature dependence( ~ T−0.34), in sharp contrast to the conventional ~T−1 dependence. Particularly, the vibrational properties of Cs2AgBiBr6 are featured by strong anharmonicity and wave-like tunnelling of phonons. Anharmonic phonon renormalization from both the cubic and quartic anharmonicities are found essential in precisely predicting the phase transition temperature in Cs2AgBiBr6 while the negative phonon energy shifts induced by cubic anharmonicity has a significant influence on particle-like phonon propagation. Further, the contribution of the wave-like tunnelling to the total thermal conductivity surpasses that of the particle-like propagation above around 310 K, indicating the breakdown of the phonon gas picture conventionally used in the Peierls-Boltzmann Transport Equation. Importantly, further including four-phonon scatterings is required in achieving the dominance of wave-like tunnelling, as compared to the dominant particle-like propagation channel when considering only three-phonon scatterings. Our work highlights the importance of lattice anharmonicity and wave-like tunnelling of phonons in the thermal transport in lead-free halide double perovskites.

Strain-Driven High Thermal Conductivity in Hexagonal Boron Phosphide Monolayer.

Two-dimensional graphenelike material, hexagonal boron phosphide (h-BP), is a promising candidate for electronic and optoelectronic devices because of its suitable band gap and high carrier mobility. Especially from the ultrahigh lattice thermal conductivity (κl), it exhibits great potential to solve the challenges of future thermal management applications. Here, the excellent lattice thermal transport properties of the h-BP monolayer are systematically analyzed at the atomic level based on the first-principles method. The results show that the ultrahigh κl value of the h-BP monolayer is attributed to its high phonon group velocity and long phonon lifetime and the strong phonon hydrodynamic effect. We further explore the influence of the tensile strain on the thermal transport properties of the h-BP monolayer. As the strain increases from 0 to 8%, the κl value shows a trend of first increasing and then decreasing due to the coeffect of strain-driven changes for phonon harmonicity and anharmonicity. Under a strain of 6%, the κl value of the h-BP monolayer is as high as 795 W/mK at 300 K, which is about 2.22 times larger than that of 357 W/mK without strain. Such a significant increase in the κl value is mainly due to the increased phonon group velocity and decreased Grüneisen parameter caused by strain. This work is helpful to understand the critical role of tensile strain in lattice thermal transport of two-dimensional graphenelike materials. It is conducive to promoting the thermal management application of the h-BP monolayer.

Role of atypical temperature-responsive lattice thermal transport on the thermoelectric properties of antiperovskites Mg3XN (X = P, As, Sb, Bi)

Antiperovskite materials have garnered significant attention due to their rich array of physical properties. In this study, we undertake a theoretical exploration into the phase stabilities, and the thermal and electronic transport properties of magnesium-based antiperovskite Mg3XN (X = P, As, Sb, and Bi) based on density functional theory (DFT) calculations, aiming at designing promising thermoelectric materials. The Mg3PN and Mg3AsN possess potential lattice distortion and strong quartic anharmonicity associated with the tilting displacement of Mg6N octahedra. After phonon renormalization, the thermal conductivity of Mg3PN and Mg3AsN exhibits relatively subdued temperature responsiveness with T−0.47 and T−0.62, respectively. Of note, the thermal conductivity of Mg3BiN drops the lowest at 900 K because of its distinctive rattle-dominated flat vibrational modes and strong temperature responsiveness with T−0.96, despite having a high initial value. Moreover, the combination of multiple degeneracy pockets and lighter dispersion band edges in Mg3XN ensures high Seebeck coefficient and impressive electronic conductivity, respectively. Ultimately, Mg3BiN achieves the optimal power factor, which also guarantees its excellent thermoelectric performance with the ZT values of 1.03 and 1.01 for n-type and p-type at 900 K, respectively. Our findings shed light on the significant impact of unconventional temperature-responsive lattice thermal conductivity on thermoelectric materials for high-temperature applications.

Study on lattice dynamics and thermal conductivity of fluorite AF2 (A = Ca, Sr, Ba) based on first principles calculations.

Fluorite materials have received particular attention in electron optics due to their favorable optical properties. However, further exploration of these materials in the thermoelectric (TE) field is hampered by the lack of studies on their lattice thermal transport properties. In this work, we use first-principles calculations, combined with self-consistent phonon theory, compressive sensing lattice dynamics and the Boltzmann transport equation, to study the microscopic mechanism of lattice thermal transport properties in AF2 (A = Ca, Sr, Ba) with a fluorite structure. We investigate the effects of three-phonon and four-phonon scattering and quartic anharmonic renormalization of phonon frequencies on this system. The results show that the bonding strength of atoms A (Ca, Sr, and Ba) plays an important role in the thermal transport process, and the third-order anharmonicity also plays an important role in this system. Meanwhile, the role of the quartic anharmonicity cannot be ignored. Our findings not only fill in the gaps in the study of lattice thermal transport of fluorite materials, but also deepen the comprehensive understanding of the high κL value of fluorite materials.

High throughput screening of semiconductors with low lattice thermal transport induced by long-range interactions.

Semiconductors with long-range interactions (LRI) due to resonant bonding exhibit delocalized electronic states and low lattice thermal conductivity, contributing to the efficiency of heat-to-electricity conversion. Here, we build a descriptor for high-throughput screening of LRI materials from the second-order interaction force constants. We identify 75 semiconducting candidates from the binary compounds in the MatHub-3d database that contain LRI. By analyzing the bonding properties of LRI atoms, we classify LRI in materials into two categories: type I and type II. In the structural unit of type I LRI, the atoms have strong bond connections, while a weak bond exists between the two groups in the structural unit of type II LRI. We have identified atypical type I LRI formed by Sb-Sb and Mg-Mg pairs in the emerging thermoelectric material Mg3Sb2, resulting in the softening of TA1 phonons and large anharmonicity. For type II LRI, the LRI of Ge-Ge and Se-Se pairs in R3m-GeSe can cross different layers. Moreover, we observe a combination of type II LRI and rattling effect in BaSe2 to restrict thermal transport. This work is of great significance for understanding the relationship between LRI and thermal transport properties, and for designing new LRI-induced low lattice thermal conductivity materials.

Polytelluride square planar chain-induced anharmonicity results in ultralow thermal conductivity and high thermoelectric efficiency in Al2Te5 monolayers.

Two-dimensional (2D) metal chalcogenides provide rich ground for the development of nanoscale thermoelectrics, although achieving optimal thermoelectric efficiency is still a challenge. Here, we leverage the unique chemistry of tellurium (Te), renowned for its hypervalent bonding and catenation abilities, to tackle this challenge as manifested in Al2Te3 and Al2Te5 monolayers. While the former forms a straightforward covalent Al-Te network, the latter adopts a more intricate bonding mechanism, enabled by eccentric features of Te chemistry, to maintain charge balance. In Al2Te5, a square planar chain (SPC) known as polytelluride [Te3]2- is neutralized by the covalently bonded [Al2Te2]2+ framework. The hypervalent nature of Te results in bizarre Born effective charges of 7 and -4 for adjacent Te atoms within the square planar chain, a feature that induces significant anharmonicity in Al2Te5 monolayers. Enhanced anharmonic lattice vibrations and the accordion pattern bestow glass-like, strongly anisotropic thermal conductivity to the Al2Te5 monolayer. The calculated κL values of 1.8 and 0.5 W m-1 K-1 along the a- and b-axes at 600 K are one order of magnitude lower than those of Al2Te3, and even lower than monolayers that contain heavy cations like Bi2Te3. Moreover, the tellurium chain dominates the valence band maximum and conduction band minimum of Al2Te5, leading to a high valley degeneracy of 10, and thus a high power factor and figure of merit (zT). Using rigorous first-principles calculations of electron relaxation time, the estimated hole-doped and electron-doped zT of, respectively, 1.5 and 0.5 at 600 K is achieved for Al2Te5. The pioneering zT of Al2Te5 compared to that of Al2Te3 is rooted merely in its amorphous-like lattice thermal transport and its polytelluride chain. These findings underscore the importance of aluminum telluride and polymeric-based inorganic compounds as practical and cost-effective thermoelectric materials, pending further experimental validation.

Investigation of the lattice thermal transport properties of Janus XClO (X = Cr, Ir) monolayers by first-principles calculations.

In the context of the global energy crisis, the development of high-performance heat transport devices within nano scales has become increasingly important. Theoretical discovery and evaluation of novel structures with high performance in thermal conductivity by affordable calculations could provide significant instructions for experimental studies focusing on thermoelectric device development. For 2-dimensional (2D) functional materials, their heat transport efficiency is correlated with their electronic properties and structural features. In this study, we computationally investigated the heat transport within Janus XClO (X = Cr, Ir); its structural and electronic properties were well solved by first-principles calculations. Furthermore, to evaluate thermodynamics stability and applicability, ab initio molecular dynamics (AIMD) simulations are conducted. Through a benchmarking study upon these XClO monolayers with different compositions, we noticed that their heat transport efficiency is associated with the percentage of doped magnetic atoms. The theoretical insights provided by this study are highly instructive for future experimental studies focusing on thermal device development.

Computational study of lattice and thermoelectric properties of Rb2LiTlF6 double perovskite

We applied the density functional theory formalism to compute the lattice thermal conductivity, transport and thermoelectric properties of Rb2LiTlF6 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.

Diameter-dependent ultra-high thermoelectric performance of ZnO nanowires

Zinc oxide (ZnO) shows great potential in electronics, but its large intrinsic thermal conductivity limits its thermoelectric applications. In this work, we explore the significant carrier transport capacity and diameter-dependent thermoelectric characteristics of wurtzite-ZnO 〈0001〉 nanowires based on first-principles and molecular dynamics simulations. Under the synergistic effect of band degeneracy and weak phonon–electron scattering, P-type (ZnO)73 nanowires achieve an ultra-high power factor above 1500 μW⋅cm−1⋅K−2 over a wide temperature range. The lattice thermal conductivity and carrier transport properties of ZnO nanowires exhibit a strong diameter size dependence. When the ZnO nanowire diameter exceeds 12.72 Å, the carrier transport properties increase significantly, while the thermal conductivity shows a slight increase with the diameter size, resulting in a ZT value of up to 6.4 at 700 K for P-type (ZnO)73. For the first time, the size effect is also illustrated by introducing two geometrical configurations of the ZnO nanowires. This work theoretically depicts the size optimization strategy for the thermoelectric conversion of ZnO nanowires.

Thermal conductivity of van der Waals heterostructure of 2D GeS and SnS based on machine learning interatomic potential

van der Waals heterostructures have provided an unprecedented platform to tune many physical properties for two-dimensional materials. In this work, thermal transport properties of van der Waals heterostructures formed by vertical stacking of monolayers GeS and SnS have been investigated systematically based on machine learning interatomic potential. The effect of van der Waals interface on the lattice thermal transport of 2D SnS and GeS can be well clarified by introducing various stacking configurations. Our results indicate that the van der Waals interface can strongly suppress the thermal transport capacity for the considered heterostructures, and either the average thermal conductivity per layer or the 2D thermal sheet conductance for the considered heterostructures is lower than that of corresponding monolayers. The suppressed thermal conductivity with tunable in-plane anisotropy in SnS/GeS heterostructures can be ascribed to the enhanced interface anharmonic scattering, and thus exhibits obvious interface-dependent characteristics. Therefore, this work highlights that the van der Waals interface can be employed to effectively modulate thermal transport for the 2D puckered group-IV monochalcogenides, and the suppressed lattice thermal conductivity together with interface-dependent phonon transport properties in the SnS/GeS heterostructure imply the great potential for corresponding thermoelectrical applications.

Lattice dynamics and thermal transport of PbTe under high pressure

Lattice dynamics and thermal transport of PbTe under high pressure

FIRST-PRINCIPLES STUDY OF THE LATTICE THERMAL CONDUCTIVITY OF MoSi2P4 AND WSi2P4 MONOLAYERS

Recently, the 2D van der Waals (vdW) layered MA2Z4 series has attracted a lot of attention. Among these 2D materials, MoSi2P4 and WSi2P4 monolayers each demonstrate strong environmental stability, a moderate band gap, and considerable carrier mobility. The lattice thermal transport properties in MoSi2P4 and WSi2P4 monolayer structures have been investigated using first-principles calculations. Due to the gap present in the phonon energy band structure of the WSi2P4 monolayer within the middle frequency range, the specific heat capacity, phonon group velocity, and phonon relaxation time of the WSi2P4 monolayer structure are smaller than those of the MoSi2P4 monolayer structure. This makes the lattice thermal conductivity of the WSi2P4 monolayer lower than that of the MoSi2P4 monolayer. The MoSi2P4 structure has a lattice thermal conductivity of 28 W/mK at 300 K. The WSi2P4 structure has a lattice thermal conductivity of 14.5 W/mK in the [Formula: see text] -direction and 15 W/mK in the [Formula: see text]-direction. The results suggest that the MoSi2P4 and WSi2P4 monolayers can be potentially used as nanoelectronics devices for thermal transport applications.

Lattice Dynamics and Thermal Transport in Semiconductors with Anti-Bonding Valence Bands.

Achieving high thermoelectric performance requires efficient manipulation of thermal conductivity and a fundamental understanding of the microscopic mechanisms of phonon transport in crystalline solids. One of the major challenges in thermal transport is achieving ultralow lattice thermal conductivity. In this study, we use the anti-bonding character of the highest-occupied valence band as an efficient descriptor for discovering new materials with an ultralow thermal conductivity. We first examined the relationship between anti-bonding valence bands (ABVBs) and low lattice thermal conductivity in model systems PbTe and CsPbBr3. Then, we conducted a high-throughput search in the Materials Project database and identified over 600 experimentally stable binary semiconductors with an anti-bonding character in their valence bands. From our candidate list, we conducted a comprehensive analysis of the chemical bonds and the thermal transport in the XS family, where X = K, Rb, and Cs are alkaline metals. These materials all exhibit ultralow thermal conductivities less than 1 W/(m K) at room temperature despite simple structures. We attributed the ultralow thermal conductivity to the weakened bonds and increased phonon anharmonicity due to their ABVBs. Our results provide chemical intuitions to understand lattice dynamics in crystals and open up a convenient venue toward searching for materials with an intrinsically low lattice thermal conductivity.