Ultralow Lattice Thermal Conductivity Research Articles

DFT study of double perovskites Cs2AgBiX6 (X = Cl, Br): An alternative of hybrid perovskites

The double perovskites are promising materials for renewable energy to fulfil the challenges of energy requirements in the world. Therefore, in this article, the optical, thermoelectric, thermodynamic, and mechanical properties of Cs2AgBiX6 (X ​= ​Cl, Br) are addressed comprehensively by the DFT approach. The stabilities regarding structure, and thermodynamics are ensured by findings of tolerance factor, and formation energy. The mechanical stability and ductile nature has been confirmed from elastic constants, Passion's, and Pugh's rules. The hardness, Debye temperature, longitudinal and transverse velocities of sounds are also explained for thermodynamic behavior understanding. The band gap for Cs2AgBiCl6 is 2.76 ​eV, which reduces to 1.9 ​eV by changing Cl with Br due to pd-hybridization of anions and cations. The optical characteristics are elaborated by dielectric constants, absorption, refractive index, and reflectivity. The absorption in visible and ultraviolet regions make them significantly important for solar cells. The ultralow lattice thermal conductivity and high figure of merit have been computed due to large Seebeck coefficient and electrical conductivity.

Cross-scale porous structure design leads to optimized thermoelectric performance and high output power for CaMnO3 ceramics and their uni-leg modules

In this work, three kinds of cross-scale pores with nano-, micro-, and sub-millimeter scales are designed and successfully synthesized in the same composition of Ca0.96Dy0.02Yb0.02MnO3, and the effects of pore structures with different scales on the performance of thermoelectric materials and uni-leg power generation modules are studied. The average pore sizes (porosities) of these three porous ceramics are about 500 nm (6.0%), 3 μm (28.0%), and 400 μm (68.8%), respectively. It is a notable result, the thermal conductivity downfall sharply with the increasing of pore size and porosity, and an ultra-low lattice thermal conductivity κL of 0.39 W/mK is obtained for submillimeter-porous ceramic owing to multiple phonon scattering and boundary effect of sub-millimeter pores. The achieved lowest value of thermal conductivity can meet the level of insulation bricks. Combining the relative higher power factor, the highest zT of 0.19 is obtained for CaMnO3 thermoelectric sample with micro-scale pores. The highest output power density of pa = 104.94 mW·cm−2 and thermoelectric efficiency factor of ϕ = 0.54 µW·cm−2·K−2 are obtained for thermoelectric module fabricated by nano-porous ceramics, due to the lower contact resistance and enhanced thermoelectric properties of the material, which is far greater than that of most reported CaMnO3 modules. As above finds, the optimal values of κL, zT, pa and ϕ correspond to the three kinds of pores. So trying to exert all advantages of three kinds of pores synergistically in the future further enhances the thermoelectric performance for porous oxide materials and modules simultaneously.

Mapping Thermoelectric Transport in a Multicomponent Alloy Space

AbstractInterest in high entropy alloy thermoelectric materials is predicated on achieving ultralow lattice thermal conductivity κL through large compositional disorder. However, here it is shown that for a given mechanism, such as mass contrast phonon scattering, κL will be minimized along the binary alloy with highest mass contrast, such that adding an intermediate mass atom to increase atomic disorder can increase thermal conductivity. Only when each component adds an independent scattering mechanism (such as adding strain fluctuation to an existing mass fluctuation) is there a benefit. In addition, both charge carriers and heat‐carrying phonons are known to experience scattering due to alloying effects, leading to a trade‐off in thermoelectric performance. Analytic transport models are applied, based on perturbation and effective medium theories, to predict how alloy scattering will affect the thermal and electronic transport across the full compositional range of several pseudo‐ternary and pseudo‐quaternary alloy systems. To do so, a multicomponent extension is demonstrated to both thermal and electronic binary alloy scattering models based on the virtual crystal approximation. Finally, it is shown that common functional forms used in computational thermodynamics can be applied to this problem to further generalize the scattering behavior that is modeled.

Higher-order anharmonicity leads to ultra-low thermal conductivity and high output power density of SnTe-based thermoelectric materials and modules

Higher-order anharmonicity is found in copper and manganese doped tin telluride (SnTe) alloys, and its effect on thermoelectric performance is systematically studied. Analyzation of thermal expansion shows that the ionic potential not only consists of cubic term, but also quartic term. Short phonon lifetime derived from more diffused peak of Brillouin spectrometer results from the higher-order anharmonicity. As a result, an ultra-low lattice thermal conductivity of 0.5 Wm−1K−1 is achieved. Soft optical phonon mode was observed from Raman spectrometer, the transverse optical - longitudinal acoustic phonon interaction may be the reason for the enhanced anharmonicity. Combining with the enlarged power factor caused by band convergence, the highest figure of merit reaches 1.3 at 873 K for doped samples. Additionally, the large temperature difference of 600 K and high output power densities of 291 mWmm−3 of simulated SnTe uni-leg module are achieved. This work supplies way for revealing the anharmonicity experimentally, and proves modification of intrinsic anharmonicity is an avenue for enhancing the thermoelectric performance of SnTe alloys.

XTlO (X = K, Rb, Cs): Novel 2D semiconductors with high electron mobilities, ultra-low lattice thermal conductivities and high thermoelectric figures of merit at room temperature

Thermoelectric materials have attracted much attention in recent years because of their potential application prospects in clean energy and waste heat utilization. In this work, we proposed three novel two-dimensional materials, namely KTlO, RbTlO and CsTlO. Based on the state-of-the-art first principles calculation methods, we found that the three monolayers shown high stability, and with indirect band-gaps of 2.31 eV, 2.27 eV and 2.48 eV, respectively. Their carrier mobilities showed obvious anisotropy, with electron and hole mobilities reaching ∼103 and ∼102 cm2·V−1·s−1, respectively. In addition, the monolayers shown large Seebeck coefficient (1.75 ∼ 2.09 mV·K−1), high conductivities (106 ∼ 108 Ω-1m−1), as well as power factor (3.19 ∼ 52.19 mW·K-2·m−1). Also, the monolayers possess ultra-low lattice thermal conductivities of 0.32 ∼ 0.51 W·m−1·K−1. As results, their ZT values are up to 1.22, 1.41 and 1.24 at 300 K, respectively. All these properties indicate that monolayer XTlO (X = K, Rb, Cs) have promising applications in the fields of microelectronic devices and thermoelectric materials.

Insights into Low Thermal Conductivity in Inorganic Materials for Thermoelectrics.

Efficient manipulation of thermal conductivity and fundamental understanding of the microscopic mechanisms of phonon scattering in crystalline solids are crucial to achieve high thermoelectric performance. Thermoelectric energy conversion directly and reversibly converts between heat and electricity and is a promising renewable technology to generate electricity by recovering waste heat and improve solid-state refrigeration. However, a unique challenge in thermal transport needs to be addressed to achieve high thermoelectric performance: the requirement of crystalline materials with ultralow lattice thermal conductivity (κL). A plethora of strategies have been developed to lower κL in crystalline solids by means of nanostructural modifications, introduction of intrinsic or extrinsic phonon scattering centers with tailored shape and dimension, and manipulation of defects and disorder. Recently, intrinsic local lattice distortion and lattice anharmonicity originating from various mechanisms such as rattling, bonding heterogeneity, and ferroelectric instability have found popularity. In this Perspective, we outline the role of manipulation of chemical bonding and structural chemistry on thermal transport in various high-performance thermoelectric materials. We first briefly outline the fundamental aspects of κL and discuss the current status of the popular phonon scattering mechanisms in brief. Then we discuss emerging new ideas with examples of crystal structure and lattice dynamics in exemplary materials. Finally, we present an outlook for focus areas of experimental and theoretical challenges, possible new directions, and integrations of novel techniques to achieve low κL in order to realize high-performance thermoelectric materials.

Honeycomb-like puckered PbTe monolayer: A promising n-type thermoelectric material with ultralow lattice thermal conductivity

Inspired by the superior thermoelectric performance of two-dimensional (2D) materials, the electrical transport and thermoelectric properties of honeycomb-like puckered PbTe monolayer were theoretically evaluated using the first-principles calculations and the semiclassical Boltzmann transport theory. The puckered PbTe monolayer is a direct gap semiconductor with wide bandgap of 2.251 eV within Heyd-Scuseria-Ernzerhof (HSE06) hybrid functional in combination with spin-orbital coupling (SOC) effect. Further analysis of formation energy, elastic constant, and ab initio molecular dynamics (AIMD) simulation prove the thermodynamic, mechanical and thermal stabilities of PbTe monolayer. The low thermal transport, small phonon group velocity, large Grüneisen parameters, and short phonon relaxation time greatly suppress the phonon transport and lead to low lattice thermal conductivity of ∼0.75 and ∼0.79 W/m K along the armchair and zigzag directions at 900 K, respectively. An optimal ZT = ~1.55 at the carrier concentration of 3.94 × 10 12 cm −2 is obtained for PbTe monolayer along zigzag direction at 900 K, which demonstrates the great advantages of honeycomb-like puckered PbTe monolayer as promising n- type thermoelectric material. Our present results would not only provide fundamental understanding of thermoelectric transport in honeycomb-like puckered PbTe monolayer, but also shed some light on the theoretical design of low dimensional PbTe-layered nanomaterials in thermoelectric applications. The honeycomb-like puckered PbTe monolayer with ultralow lattice thermal conductivity was designed for n -type thermoelectric material with excellent energy conversion efficiency. • The PbTe monolayer is direct semiconductor with wide band gaps. • The honeycomb-like puckered PbTe monolayer is dynamically and mechanically, and thermally stable. • The PbTe monolayer has low thermal conductivity, especially along armchair direction. • The puckered PbTe monolayer possesses excellent electron transport properties and power factor. • The n -type PbTe monolayer exhibit good thermoelectric properties, which can be used as potential materials for thermoelectric applications.

The ultra-low lattice thermal conductivity dominated by the quartic anharmonicity in Bi-based binary compounds A3Bi (A = K, Rb)

In this article, by using self-consistent phonon (SCP) theory, compressed sensing (CS) technology and Boltzmann transport equation (BTE), we studied the role of quartic anharmonicity in the lattice dynamics and thermal transport characteristics of Bi-based binary compounds A3Bi (A = K, Rb), with a particular focus on unraveling the impacts of quartic anharmonicity on lattice thermal conductivity . By analyzing the phonon dispersion curve and the phonon density of states, we found that the strong quartic anharmonicity, which is mainly caused by the alkali metal atoms A1 in A3Bi (A = K, Rb), hardens the vibration frequency of the low-lying phonon branch and ensures the lattice dynamic stability. Through the relaxation time approximation of the Boltzmann transport equation, the calculated considering the three-phonon (3ph) and four-phonon (4ph) scattering process shows an ultra-low value. In addition, we also conducted a detailed analysis of the normalized lattice thermal conductivity, phonon group velocity, phonon scattering rate, and scattering phase space, revealing that the extremely low in A3Bi is mainly due to its relatively strong 4ph scattering process. Our research proves the existence of strong quartic anharmonicity in A3Bi, and we have studied in detail the influence of 3ph and 4ph scattering processes on the thermal transport properties of A3Bi, which has never been reported before.

Enhanced thermoelectric performance of n-type (PbSe)n(Sb2Te3) pseudo-binary via Zn filling and Ag2Se compositing

Lead selenide (PbSe) is considered to be decent candidate replacing lead telluride (PbTe) as intermediate temperature (600–900 K) thermoelectric application due to its lower intrinsic lattice thermal conductivity, higher thermal stability, and larger abundance of Se than Te. To improve the thermoelectric performance of n-type PbSe, we constructed an n-type PbSe-Sb2Se3 pseudo-binary via alloying Sb2Se3 into PbSe matrix to obtain a reduced lattice thermal conductivity at a broad temperature range. Next, we introduced extra Zn into matrix to optimize the electron concentration. Last, we further added excess Ag2Se to modulate the lattice thermal conductivity at temperature< 523 K. Eventually, we obtained an ultralow lattice thermal conductivity of ~ 0.40 W m−1 K−1 and a large peak ZT of ~ 1.36 at 773 K in the composition of (PbSe)40(Sb2Se3)Zn0.1(Ag2Se)0.75; meanwhile, the average ZT between 323 and 773 K is as high as ~ 0.78, revealing a significant improvement over pristine PbSe.

Lone-Pair-Like Interaction and Bonding Inhomogeneity Induce Ultralow Lattice Thermal Conductivity in Filled β-Manganese-Type Phases.

Finding a way to interlink heat transport with the crystal structure and order/disorder phenomena is crucial for designing materials with ultralow lattice thermal conductivity. Here, we revisit the crystal structure and explore the thermoelectric properties of several compounds from the family of the filled β-Mn-type phases M2/nn+Ga6Te10 (M = Pb, Sn, Ca, Na, Na + Ag). The strongly disturbed thermal transport observed in the investigated materials originates from a three-dimensional Te–Ga network with lone-pair-like interactions, which results in large variations of the Ga–Te and M–Te interatomic distances and substantial anharmonic effects. In the particular case of NaAgGa6Te10, the additional presence of different cations leads to bonding inhomogeneity and strong structural disorder, resulting in a dramatically low lattice thermal conductivity (∼0.25 Wm–1 K–1 at 298 K), being the lowest among the reported β-Mn-type phases. This study offers a way to develop materials with ultralow lattice thermal conductivity by considering bonding inhomogeneity and lone-pair-like interactions.

SnSe nanoparticles with the ultra-low lattice thermal conductivity: synthesis and characterization

SnSe nanoparticles with the ultra-low lattice thermal conductivity: synthesis and characterization

Theoretical prediction of mechanics, transport, and thermoelectric properties of full Heusler compounds Na2KSb and X2CsSb (X=K,Rb)

Full Heusler compounds have become a research hotspot in the thermoelectric (TE) field, because they have the remarkable electronic properties and high-TE power factor. Nevertheless, the inherent high thermal conductivity ${\ensuremath{\kappa}}_{L}$ hinders their further application as TE device. Hence, we investigate the mechanical, transport, and thermoelectric properties in ${\mathrm{Na}}_{2}\mathrm{KSb}$ and ${\mathrm{X}}_{2}\mathrm{CsSb}$ (X = K, Rb) with eight valence electrons per formula unit (f.u.) by using the first-principles calculations combined with self-consistent phonon (SCP) theory, compressive sensing (CS) techniques, and Boltzmann transport equation (BTE). Due to the strong three phonon scattering combined with small phonon group velocity, we obtain the ultralow lattice thermal conductivities. An evaluation of their mechanical properties reveals that they are all brittle compounds, and ${\mathrm{Rb}}_{2}\mathrm{CsSb}$ has the strongest elastic anisotropy. To capture rational electron transport properties, we include the effects of the acoustic deformation potential (ADP) scattering, polar optical phonon (POP) scattering, and ionized impurity (IMP) scattering on the electron relaxation time. Finally, a high p-type $\mathit{ZT}$ values of 2.74 (2.48) at 600 (900) K are captured in the cubic ${\mathrm{K}}_{2}\mathrm{CsSb}$ $({\mathrm{Na}}_{2}\mathrm{KSb})$. These findings not only help us to comprehensively understand the physical properties of full Heusler compounds with eight valence electrons per f.u., but also support them as potential candidates for thermal management and thermoelectric applications.

Hidden Local Symmetry Breaking in Silver Diamondoid Compounds is Root Cause of Ultralow Thermal Conductivity

AbstractTypically, conventional structure transitions occur from a low symmetry state to a higher symmetry state upon warming. In this work, an unexpected local symmetry breaking in the tetragonal diamondoid compound AgGaTe2 is reported, which, upon warming, evolves continuously from an undistorted ground state to a locally distorted state while retaining average crystallographic symmetry. This is a rare phenomenon previously referred to as emphanisis. This distorted state, caused by the weak sd3 orbital hybridization of tetrahedral Ag atoms, causes their displacement off the tetrahedron center and promotes a global distortion of the crystal structure resulting in strong acoustic–optical phonon scattering and an ultralow lattice thermal conductivity of 0.26 W m−1 K−1 at 850 K in AgGaTe2. The findings explain the underlying reason for the unexpectedly low thermal conductivities of silver‐based compounds compared to copper‐based analogs and provide a guideline to suppressing heat transport in diamondoid and other materials.

Strongly Anharmonic Phonons and Their Role in Superionic Diffusion and Ultralow Thermal Conductivity of Cu7PSe6

AbstractThe quest for advanced superionic materials requires understanding their complex atomic dynamics, but detailed studies of the interplay between lattice vibrations and ionic diffusion remain scarce. Here inelastic and quasielastic neutron scattering measurements in the superionic argyrodite Cu7PSe6 are reported, combined with molecular dynamics (MD) based on ab initio and machine‐learned potentials, providing critical insights into the atomistic mechanisms underlying fast ion conduction. The results reveal how long‐range Cu diffusion is limited by intercluster hopping, controlled by selective anharmonic phonons of the crystalline framework. Further, the Green–Kubo simulations reproduce the ultralow lattice thermal conductivity and identify contributions from mobile ions, phonons, and their cross‐correlations. The mode resolved analysis shows that the thermal conductivity is dominated by low‐energy acoustic phonon modes of the overall crystal framework. The analysis of mode‐resolved spectral functions further show that vibrational modes with significant Cu contributions are strongly damped, corresponding to the breakdown of associated phonon quasiparticles. These results highlight the importance of strongly anharmonic effects in superionic systems, in which the traditional quasiharmonic phonon picture is insufficient, and pave the way toward combining machine‐learning accelerated simulations with neutron scattering experiments to rationalize the complex atomic dynamics underlying ionic and thermal transport.

Zintl Phase Compounds Mg3Sb2−xBix (x = 0, 1, and 2) Monolayers: Electronic, Phonon and Thermoelectric Properties From ab Initio Calculations

The Mg3Sb2−xBix family has emerged as the potential candidates for thermoelectric applications due to their ultra-low lattice thermal conductivity (κL) at room temperature (RT) and structural complexity. Here, using ab initio calculations of the electron-phonon averaged (EPA) approximation coupled with Boltzmann transport equation (BTE), we have studied electronic, phonon and thermoelectric properties of Mg3Sb2−xBix (x = 0, 1, and 2) monolayers. In violation of common mass-trend expectations, increasing Bi element content with heavier Zintl phase compounds yields an abnormal change in κL in two-dimensional Mg3Sb2−xBix crystals at RT (∼0.51, 1.86, and 0.25 W/mK for Mg3Sb2, Mg3SbBi, and Mg3Bi2). The κL trend was detailedly analyzed via the phonon heat capacity, group velocity and lifetime parameters. Based on quantitative electronic band structures, the electronic bonding through the crystal orbital Hamilton population (COHP) and electron local function analysis we reveal the underlying mechanism for the semiconductor-semimetallic transition of Mg3Sb2-−xBix compounds, and these electronic transport properties (Seebeck coefficient, electrical conductivity, and electronic thermal conductivity) were calculated. We demonstrate that the highest dimensionless figure of merit ZT of Mg3Sb2−xBix compounds with increasing Bi content can reach ∼1.6, 0.2, and 0.6 at 700 K, respectively. Our results can indicate that replacing heavier anion element in Zintl phase Mg3Sb2−xBix materials go beyond common expectations (a heavier atom always lead to a lower κL from Slack’s theory), which provide a novel insight for regulating thermoelectric performance without restricting conventional heavy atomic mass approach.

Monolayer SnI2: An Excellent p-Type Thermoelectric Material with Ultralow Lattice Thermal Conductivity.

Using density functional theory and semiclassical Boltzmann transport equation, the lattice thermal conductivity and electronic transport performance of monolayer SnI2 were systematically investigated. The results show that its room temperature lattice thermal conductivities along the zigzag and armchair directions are as low as 0.33 and 0.19 W/mK, respectively. This is attributed to the strong anharmonicity, softened acoustic modes, and weak bonding interactions. Such values of the lattice thermal conductivity are lower than those of other famous two-dimensional thermoelectric materials such as MoO3, SnSe, and KAgSe. The two quasi-degenerate band valleys for the valence band maximum make it a p-type thermoelectric material. Due to its ultralow lattice thermal conductivities, coupled with an ultrahigh Seebeck coefficient, monolayer SnI2 possesses an ultrahigh figure of merits at 800 K, approaching 4.01 and 3.34 along the armchair and zigzag directions, respectively. The results indicate that monolayer SnI2 is a promising low-dimensional thermoelectric system, and would stimulate further theoretical and experimental investigations of metal halides as thermoelectric materials.

The prediction of electronic and thermoelectric performance of bulk and monolayer Sb2TeSeS

The thermoelectric (TE) properties of the bulk and monolayer Sb2TeSeS have been studied by the first-principles calculations and the Boltzmann Transport theory. Due to the greater band gap, the absolute values of Seebeck coefficient for TB-mBJ potential at the vicinity of Fermi level are larger than that for GGA approach. It is found that the electronic thermal conductivity of the layered structure of Sb2TeSeS is relatively lower than that of the bulk compounds. It is stable for monolayer Sb2TeSeS on account of the phonon structure without imaginary frequency, and the phonon dispersion is comparatively flatter. It is expected the ultra-low lattice thermal conductivity, which is verified by the result of the calculated lattice thermal conductivity. For monolayer Sb2TeSeS, the maximum value of figure of merit, which is procured from p-type doping within the reasonable range of carrier concentration, is larger than the optimal ZT value of other well-known materials. Therefore, p-type doping of monolayer Sb2TeSeS is a potential candidate for TE device applications.

CoFeVSb: A promising candidate for spin valve and thermoelectric applications

We report a combined theoretical and experimental study of a novel quaternary Heusler system CoFeVSb from the view point of room temperature spintronics and thermoelectric applications. It crystallizes in cubic structure with small DO$_3$-type disorder. The presence of disorder is confirmed by room temperature synchrotron X-ray diffraction(XRD) and extended X-ray absorption fine structure (EXAFS) measurements. Magnetization data reveal high ordering temperature with a saturation magnetization of 2.2 $\mu_B$/f.u. Resistivity measurements reflect half-metallic nature. Double hysteresis loop along with asymmetry in the magnetoresistance(MR) data reveals room temperature spin-valve feature, which remains stable even at 300 K. Hall measurements show anomalous behavior with significant contribution from intrinsic Berry phase. This compound also large room temperature power factor ($\sim0.62$ mWatt/m/K$^{2}$) and ultra low lattice thermal conductivity ($\sim0.4$ W/m/K), making it a promising candidate for thermoelectric application. Ab-initio calculations suggest weak half-metallic behavior and reduced magnetization (in agreement with experiment) in presence of DO$_3$ disorder. We have also found an energetically competing ferromagnetic FM)/antiferromagnetic (AFM) interface structure within an otherwise FM matrix: one of the prerequisites for spin valve behavior. Coexistence of so many promising features in a single system is rare, and hence CoFeVSb gives a fertile platform to explore numerous applications in future.

An optimum thermoelectric figure of merit using Ge2Se2 monolayer: An ab-initio approach

It is found that many two-dimensional chalcogenides are exhibiting a superlative thermoelectric behavior because of their versatile characters in terms of stability, conductivity, bandgap tunability, etc. In this paper, the thermoelectric properties of monolayer Ge2Se2 have been calculated using first-principles calculations with all involved electrical and thermal transport properties in the parameter-free framework. It has been found that the Ge2Se2 offers a bandgap of 1.13 eV with a sufficiently high thermoelectric coefficient. The thermoelectric transport parameters have been calculated by solving the linearized Boltzmann Transport Equation and found optimum to qualify for good thermoelectric materials. The investigated material exhibit outstanding thermoelectric performance in terms of an ultra low lattice thermal conductivity of the order of 0.5 Wm−1K−1 and TE Figure of merit around two (2) at 1000 K. For better accuracy in results, we employed hybrid exchange–correlation (HSE06) throughout the calculations and, instead of approximating the relaxation time, computed the accurate relaxation time using the deformation potential approach. The research findings prove its excellent behavior and worthy guideline for the experimentalists looking for materials with high FoM to design thermoelectric devices.

Ultra-low lattice thermal conductivity and high figure of merit for Janus MoSeTe monolayer: a peerless material for high temperature regime thermoelectric devices

Ultra-low lattice thermal conductivity and high figure of merit for Janus MoSeTe monolayer: a peerless material for high temperature regime thermoelectric devices