Room Temperature Thermal Conductivity Research Articles

Numerical characterization of thermal transport in hexagonal tungsten disulfide (WS2) nanoribbons

In this study, we have investigated the thermal transport characteristics of single-layer tungsten disulfide, WS2 nanoribbons (SLTDSNRs) using equilibrium molecular dynamics simulations with the help of Green-Kubo formulation. Using Stillinger-Weber (SW) inter-atomic potential, the calculated room temperature thermal conductivities of 15 nm × 4 nm pristine zigzag and armchair SLTDSNRs are 126 ± 10 W m−1K−1 and 110 ± 6 W m−1K−1, respectively. We have explored the dependency of thermal conductivity on temperature, width, and length of the nanoribbon. The study shows that the thermal conductivity of the nanoribbon decreases with the increase in temperature, whereas the thermal conductivity increases with an increase in either the width or length of the ribbon. The thermal conductivity does not increase uniformly as the size of the ribbon changes. We have also observed that the thermal conductivity of SLTDSNRs depends on edge orientations; the zigzag nanoribbon has greater thermal conductivity than the armchair nanoribbon, regardless of temperature or dimension variations. Our study additionally delves into the tunable thermal properties of SLTDSNRs by incorporating defects, namely vacancies such as point vacancy, edge vacancy, and bi-vacancy. The thermal conductivities of nanoribbons with defects have been found to be considerably lower than their pristine counterparts, which aid in enhanced values for the thermoelectric figure of merit (zT). We have varied the vacancy concentration within a range of 0.1% to 0.9% and found that a point vacancy concentration of 0.1% leads to a 64% reduction in the thermal conductivity of SLTDSNRs. To elucidate these phenomena, we have calculated the phonon density of states for WS2 under different aspects. The findings of our work provide important understandings of the prospective applications of WS2 in nanoelectronic and thermoelectric devices by tailoring the thermal transport properties of WS2 nanoribbons.

Significant phonon localization and suppressed transport in silicon-doped gallium oxide: A study using a unified neural network interatomic potential

Monoclinic gallium oxide (β-Ga2O3) is a fourth-generation semiconductor with great application potential in high-power microelectronics. Recent studies indicate that the electrical conductivity of β-Ga₂O₃ can be substantially enhanced through silicon (Si) doping. However, the effects on thermal transport, especially by considering the practical nanostructures within the crystal, have not yet been explored. To address this gap, we have developed a unified neural network potential for investigating the unexplored phonon transport of the β-(SixGa1–x)2O3 with varying doping levels. Our atomistic simulations showed that compared to intrinsic β-Ga2O3, the room-temperature thermal conductivities respectively decreased by 36.5%, 33.5%, and 38.8% along the a, b, and c axes in β-SiGa511O768, and by 79.6%, 74.9%, and 77.8% in β-SiGa7O12. The significant degradation in phonon transport is attributed to increased lattice anharmonicity, reduced sound velocity, and most importantly, induced phonon localization due to Si substitutions. A quantitative analysis reveals that the localization primarily occurs in phonons with frequencies exceeding 2.5 THz. The vibration is confined to a region around the Si atom, extending only to its second-nearest neighbors.

Thermal and electrical properties of single‐phase high entropy carbide ceramics

AbstractThermal and electrical properties were investigated for five nominally phase‐pure high entropy carbide ceramics. The compositions (Hf0.2Nb0.2Ta0.2Ti0.2Zr0.2)C, (Cr0.2Hf0.2Ta0.2Ti0.2Zr0.2)C, (Hf0.2Mo0.2Ta0.2Ti0.2Zr0.2)C, (Hf0.2Ta0.2Ti0.2W0.2Zr0.2)C, and (Hf0.2Mo0.2Ti0.2W0.2Zr0.2)C were synthesized by carbothermal reduction of oxides. The thermal diffusivity and heat capacity were measured from room temperature to 1800°C. The room temperature thermal conductivity ranged from 5.1 W/mK for (Hf0.2Mo0.2Ti0.2W0.2Zr0.2)C to 9.0 W/mK for (Cr0.2Hf0.2Ta0.2Ti0.2Zr0.2)C. The thermal conductivity increased over the temperature range with maximum conductivities of 19.6 W/mK measured for (Hf0.2Mo0.2Ta0.2Ti0.2Zr0.2)C to 29.7 W/mK for (Cr0.2Hf0.2Ta0.2Ti0.2Zr0.2)C at 1800°C. The electron contribution to thermal conductivity calculated from measured electrical resistivity varied from 41% to 52% of the total thermal conductivity. The tungsten and molybdenum containing compositions had higher phonon contributions while the niobium and chromium containing compositions had nearly equal electron and phonon contributions to thermal conductivity.

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.

Lateral Heterostructure Formed by Highly Thermally Conductive Fluorinated Graphene for Efficient Device Thermal Management.

The continued miniaturization of chips demands highly thermally conductive materials and effective thermal management strategies. Particularly, the high-field transport of the devices built with 2D materials is limited by self-heating. Here a systematic control of heat flow in single-side fluorinated graphene (FG) with varying degrees of fluorination is reported, revealing a superior room-temperature thermal conductivity as high as 128W m-1 K-1. Monolayer graphene/FG lateral heterostructures with seamless junctions are approached for device fabrication. Efficient in-plane heat removal paths from graphene channel to side FG are created, contributing significant reduction of the channel peak temperature and improvement in the current-carrying capability and power density. Molecular dynamics simulations indicate that the interfacial thermal conductance of the heterostructure is facilitated by the high degree of overlap in the phonon vibrational spectra. The findings offer novel design insights for efficient heat dissipation in micro- and nanoelectronic devices.

Growth mechanism of bismuth-filled nanoporous silicon with improved structural stability and low thermal conductivity

Nano porous silicon (PS) is a strong candidate for thermoelectric application, but it shows low structural stability and is prone to collapse. To enhance the structural stability of PS and offer a new way to improve its electrical conductivity, PS was prepared by electrochemical etching and Bi nanowires were fabricated in the pores of PS by electrodeposition. In addition, for studying the effect of structures on the properties of Bi-filled PS composites, aperiodic single-layer (SL) structure, and periodic rugate (Rgt) structure and Bragg structure PS samples were prepared by changing the etching current waveform and etching time. The results show that the initial Bi deposition position and filling fraction of Bi nanowires in PS templates can be precisely controlled. Since Bi nanowires have significantly different continuity in Rgt and Bragg structures compared with SL structures, we proposed two growth mechanisms of Bi nanowires, including the axis-growth mechanism and transverse-axis-growth mechanism, with the supports of the experimental results of XRD, SEM, and EDS.The room temperature thermal conductivities of pristine and Bi-filled PS layers are in the ranges of 4.5 ∼ 5.0 and 4.2 ∼ 6.0 W･m−1K−1, respectively, about 1/10 of the original unetched silicon wafer. No apparent increase of thermal conductivity was observed in any Bi-filled composites. In addition, the thermal conductivities of PS layers with Bragg structure, including pristine and Bi-filled PS composites, are significantly lower than those of the other two structures.SEM images also demonstrates that Bi greatly improved the mechanical property of PS composites, especially the periodic structures composites. This study firmly demonstrates that Bi-filling in PS with periodic Bragg structure is practical to obtain nanocomposites with low thermal conductivity and improved structural stability. It offers a new dimension to optimize the property of PS for thermoelectric application by pore configuration design and controllable nanowire Bi filling.

Synthesis, Structure, and Properties of CuBiSeCl2: A Chalcohalide Material with Low Thermal Conductivity.

Mixed anion halide-chalcogenide materials have recently attracted attention for a variety of applications, owing to their desirable optoelectronic properties. We report the synthesis of a previously unreported mixed-metal chalcohalide material, CuBiSeCl2 (Pnma), accessed through a simple, low-temperature solid-state route. The physical structure is characterized through single-crystal X-ray diffraction and reveals significant Cu displacement within the CuSe2Cl4 octahedra. The electronic structure of CuBiSeCl2 is investigated computationally, which indicates highly anisotropic charge carrier effective masses, and by experimental verification using X-ray photoelectron spectroscopy, which reveals a valence band dominated by Cu orbitals. The band gap is measured to be 1.33(2) eV, a suitable value for solar absorption applications. The electronic and thermal properties, including resistivity, Seebeck coefficient, thermal conductivity, and heat capacity, are also measured, and it is found that CuBiSeCl2 exhibits a low room temperature thermal conductivity of 0.27(4) W K-1 m-1, realized through modifications to the phonon landscape through increased bonding anisotropy.

Tuning Thermal Conductivity of Hybrid Perovskites through Halide Alloying.

Tuning the thermal transport properties of hybrid halide perovskites is critical for their applications in optoelectronics, thermoelectrics, and photovoltaics. Here, an effective strategy is demonstrated to modulate the thermal transport property of hybrid perovskites by halide alloying. A highly tunable thermal conductivity of mixed-halide hybrid perovskites is achieved due to halide-alloying and structural distortion. The experimental measurements show that the room temperature thermal conductivity of MAPb(BrxI1- x)3 (x = 0─1) can be largely modulated from 0.27 ± 0.07W m-1 K-1 (x = 0.5) to 0.47 ± 0.09W m-1 K-1 (x = 1). Molecular dynamics simulations further demonstrate that the thermal conductivity reduction of hybrid halide perovskites results from the suppression of the mean free paths of the low-frequency acoustic and optical phonons. It is found that halide alloying and the induced structural distortion can largely increase the scatterings of optical and acoustic phonons, respectively. The confined diffusion of MA+ cations in the octahedra cage is found to act as an additional thermal transport channel in hybrid perovskites and can contribute around 10-20% of the total thermal conductivity. The findings provide a strategy for tailoring the thermal transport in hybrid halide perovskites, which may largely benefit their related applications.

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.

Preparation and properties of ZrP2O7 matrix composites with high silica fibers reinforcement

AbstractZrP2O7 ceramics exhibit poor mechanical properties after firing, as a major drawback. In this study, ZrP2O7 matrix composites reinforced with high silica fibers were prepared through pressureless sintering by varying the content and length‐to‐diameter ratio of the high silica fibers added to ZrP2O7 powder. After heat treatment at 1200‒1300°C, the room temperature flexural strength of the ZrP2O7 matrix composites with different amounts high silica fibers having different aspect ratios was 14.9‒45.2 MPa, the bulk density was 1.90‒3.03 g·cm−3, the apparent porosity was 2.37%‒39.39%, and the room temperature thermal conductivity was .47‒.95 W/(m·K). With an increase in the heat‐treatment temperature, driven by sintering and fiber crystallization, strength of the interfacial layer between the fibers and the matrix inside the ZrP2O7 matrix composites decreased and then increased. The transfer and blocking effects of the interface enabled effective transfer of the stress of the matrix to the fiber‐reinforced phase and prevented crack extension. The problem of inherent crystallization affecting high silica fibers at high temperatures was relieved by the ZrP2O7 ceramic matrix composites.

Thermal transport characterization of monolayer GaN nanoribbon doped with group IV materials: An equilibrium molecular dynamics study

Bulk gallium nitride (GaN) has been considered as one of the prominent materials for a long time in the application of laser, LED and transistors. Due to its superior electrical characteristics, its low-dimensional hexagonal counterpart is currently drawing attention like graphene. In this study, we have investigated the effect of impurity atoms on the heat energy conduction within this honeycomb nanostructure of GaN to explore its scope of applications. The room temperature thermal conductivity of zigzag GaN nanoribbon (ZGaNNR) is found to be ∼ 11 Wm−1K−1 using the molecular dynamics approach with the Green-Kubo formulation. Various group IV elements namely- carbon, silicon, germanium and tin, have been incorporated within the pristine structure in four distinct doping patterns; like- point (Type-I and Type-II), pair and delta doping, to explore the thermal transport in chemically doped nanostructures. A gradual enhancement in the thermal conductivity is observed for the increasing concentration of carbon and silicon as dopants. On the other hand, selection of germanium and tin as impurity atoms suppresses the heat conduction within the crystal due to the increased low frequency phonon scattering. In all cases, Type-I point doping affects the thermal transport of ZGaNNR significantly. The narrower ribbons impede the phonon transportation due to the strong boundary effects resulting in a lower thermal conductivity. Moreover, phonon transportation is largely suppressed, and heat energy is observed to flow at a slower rate as the temperature of the ribbon rises. We have also studied these doped structures under the influence of point, edge and pair vacancies and observed a decreasing trend in thermal conductivity for each type of vacancy defect patterns introduced in the crystal. Such a study would promote the rising interest in properly characterizing the heat transport of low dimensional nanostructures and it can be an effective technique to tune the thermal conductivity of ZGaNNR for improving thermoelectric performance and thermal management in nanoscale devices.

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.

Phonon transport properties of Janus Pb2 XAs (X = P, Sb, and Bi) monolayers: A DFT study

Grasping the underlying mechanisms behind the low lattice thermal conductivity of materials is essential for the efficient design and development of high-performance thermoelectric materials and thermal barrier coating materials. In this paper, we present a first-principles calculations of the phonon transport properties of Janus Pb2PAs and Pb2SbAs monolayers. Both materials possess low lattice thermal conductivity, at least two orders of magnitude lower than graphene and h-BN. The room temperature thermal conductivity of Pb2SbAs (0.91 W/mK) is only a quarter of that of Pb2PAs (3.88 W/mK). We analyze in depth the bonding, lattice dynamics, and phonon mode level information of these materials. Ultimately, it is determined that the synergistic effect of low group velocity due to weak bonding and strong phonon anharmonicity is the fundamental cause of the intrinsic low thermal conductivity in these Janus structures. Relative regular residual analysis further indicates that the four-phonon processes are limited in Pb2PAs and Pb2SbAs, and the three-phonon scattering is sufficient to describe their anharmonicity. In this study, the thermal transport properties of Janus Pb2PAs and Pb2SbAs monolayers are illuminated based on fundamental physical mechanisms, and the low lattice thermal conductivity endows them with the potential applications in the field of thermal barriers and thermoelectrics.

Enhancing the high-temperature thermal evacuation of Cf/C-Mo30Cu joint via grooving 3D heat transfer interface

The joining of Cf/C composite to Mo30Cu alloy plays an important practical role in a bias filter for thermonuclear fusion. In this study, the Cf/C composite is joined to Mo30Cu alloy at 860 °C/10 min using AgCu4.5Ti braze after fabricating the three dimensional (3D) heat transfer interface along the Cf/C interface. The effect of interface grooving on the thermal conductivity of the joint is investigated and compared with the original brazed joint. The results demonstrate that the room temperature thermal conductivity of the joint reached a maximum of 132 W·m−1·K−1 at a grooving depth of 200 μm, which is 17.8 % higher than that of the original joint (112 W·m−1·K−1). The thermal conductivity of the joint is still as high as 100 W·m−1·K−1 at a temperature of 500 ℃. The excellent high-temperature thermal conductivity significantly reduces the Cf/C damage and extends the service life of the joint. And the shear strength of the joint has also been significantly increased by 252 % from 13.1 MPa to 33.1 MPa. Grooves prepared along the Cf/C interface provide channels for braze penetration, increasing the contact area between the brazing seam and the Cf/C matrix. Ultimately, the thermal evacuation performance of the joint is improved by increasing the heat exchange area across the joint. Also, grooves along the Cf/C interface enable mechanical interlocking with the brazing seam, achieving an enhanced joint strength. The heat transfer process of the brazed joint is simulated and analyzed by the finite element method. The analysis indicated that the thermal evacuation across the joint can be enhanced by pre-fabricating a 3D heat transfer interface in the joint. This research can provide a reference for solving the problem of heat accumulation in the first wall materials inside thermonuclear reactors.

A flux growth technique for high quality cubic boron arsenide bulk single crystals

The growth of single crystal cubic boron arsenide (c-BAs) has attracted considerable interest due to its high room-temperature thermal conductivity and high ambipolar electrical mobility. However, currently the only growth technique reported for c-BAs crystals is the chemical vapor transport (CVT) method, which exhibits several drawbacks with regard to size scalability and crystal quality control, thereby hindering the further advancement of this semiconductor material. Herein, we report a flux growth technique using liquid arsenic (l-As) as a reaction medium at high pressures for the growth of high-quality c-BAs crystals with several millimeters size. The outstanding properties, including high uniformity, lower defect density, and lower carrier concentration of the as-grown c-BAs single crystals from flux growth, have been verified via a combination of techniques including x-ray diffraction, Raman scattering, photoluminescence spectroscopy, and electrical transport measurements, in comparison with the CVT-grown crystals.

Model Approach to Thermal Conductivity in Hybrid Graphene-Polymer Nanocomposites.

The thermal conductivity of epoxy nanocomposites filled with self-assembled hybrid nanoparticles composed of multilayered graphene nanoplatelets and anatase nanoparticles was described using an analytical model based on the effective medium approximation with a reasonable amount of input data. The proposed effective thickness approach allowed for the simplification of the thermal conductivity simulations in hybrid graphene@anatase TiO2 nanosheets by including the phenomenological thermal boundary resistance. The sensitivity of the modeled thermal conductivity to the geometrical and material parameters of filling particles and the host polymer matrix, filler's mass concentration, self-assembling degree, and Kapitza thermal boundary resistances at emerging interfaces was numerically evaluated. A fair agreement of the calculated and measured room-temperature thermal conductivity was obtained.

High-entropy (YErYbLu)2SiO5 ceramic aerogel: A potential ceramic insulator with low thermal conductivity

Conventional oxide aerogels have limitations in terms of structural damage and phase transformation at high temperatures. A novel high-entropy (YErYbLu)2SiO5 ceramic aerogel was synthesized by a combination of the sol-gel process, supercritical drying, and high-temperature calcination. The successful synthesis of a high-entropy (YErYbLu)2SiO5 ceramic aerogel in a single phase after calcination at 1250 °C was confirmed by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The high-entropy ceramic aerogel (YErYbLu)2SiO5 still shows excellent structural and phase stability after annealing at 1400 °C. The structurally reconstructed samples (RSO) exhibit low densities ranging from 1.79 to 3.28 g/cm3, room-temperature thermal conductivities between 0.109 and 0.253 W·m-1 K-1, and fracture toughness values ranging from 0.61 to 9.70 MPa. Notably, the lowest thermal conductivity is less than 1/10 of that of the corresponding dense crystalline ceramics. Furthermore, the RSO has a low coefficient of thermal expansion within the temperature range of 360–1200 °C (ranging from 5.84 × 10−6 °C−1 to 7.36 × 10−6 °C−1). The RSO exhibits high residual strength retention after thermal shock testing. These properties position the high-entropy (YErYbLu)2SiO5 ceramic aerogel as a promising candidate for nano-thermal insulation as a porous ceramic material that undergoes structural reconstruction.

Optical and thermal properties of Ge2Sb2Te5, Sb2Se3, and Sb2S3 for reconfigurable photonic devices [Invited

Phase change materials (PCMs) are one of the most promising materials candidates for reconfigurable optics owing to their two solid-state atomic structures that render distinct optical properties. Recently, there have been growing interests in integrating these materials into photonic devices for achieving reconfigurable optical properties. In this paper, we focus on examining the optical and thermal properties of three essential phase change materials: Ge2Sb2Te5, Sb2Se3, and Sb2S3. The latter two have been specifically tailored for photonic applications, with minimal absorption losses in the near-infrared spectrum. In particular, we report the optical constants, refractive index (n) and extinction coefficient (k), for 300 nm thick Ge2Sb2Te5, Sb2Se3, and Sb2S3 on CaF2 substrate across a wide spectral range of 0.3 μm to 40 μm in amorphous and crystalline states. We observe that while Ge2Sb2Te5 exhibits a larger contrast in the index of refraction upon phase transformation compared to the other two compositions, Sb2Se3 and Sb2S3 demonstrate a substantial reduction in their extinction coefficients within the infrared spectrum. In addition, using time-domain thermoreflectance (TDTR), we report their thermal conductivity as a function of temperature up to 320°C. According to our observation, the room temperature thermal conductivity of Sb2Se3 and Sb2S3 increases by almost a factor of four upon phase transformation from amorphous to crystalline. The findings of this study provides necessary parameters for modeling PCM based photonic devices and emphasize the strong potential of Sb2Se3 and Sb2S3 as promising material candidates for reconfigurable optics due to their low-loss transmission in infrared spectrum, paving the way for their practical implementation in future photonic devices.

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.