Electronic Thermal Conductivity Research Articles

Crystal structure, stability, and transport properties of Li2BeAl and Li2BeGa Heusler alloys: a DFT study

In this study, the structural, elastic, electronic, and thermoelectric properties of full Li2BeAl and Li2BeGa Heusler alloys were explored using density functional and the Boltzmann transport theories. The GGA and HSE approximations have been used for the exchange–correlation potential. Results indicated that these two compounds are more energetically stable in the inverse Heusler structure. Additionally, both Li2BeAl and Li2BeGa Heusler alloys were found to be mechanically stable due to the positive values of the elastic constants. Also, the high values of the Young's modulus indicate that these compounds are stiff and exhibit a semi-metallic nature. The band gaps were determined to be 0.13 eV and − 0.22 eV for Li2BeAl and Li2BeGa alloys, respectively, using the GGA approximation. By employing the HSE hybrid functional, however, the band gap for Li2BeAl increased to 0.26 eV, and for Li2BeGa, it decreased to − 0.16 eV. Regarding thermoelectric properties, Seebeck coefficient, electrical conductivity, electronic and lattice thermal conductivities, power factor, and the figure of merit have been calculated for both Li2BeAl and Li2BeGa Heusler alloys at different temperatures. Seebeck coefficient in both alloys decreases with increasing the temperature and has the highest value at 300 K. Thermal conductivity and electrical conductivity increase with increasing the temperature, which confirms the intermetallic behavior of the Heusler alloys. The results obtained for both alloys show that n-type doping has better thermoelectric properties than p-type doping. The maximum value of the figure of merit (ZT) was obtained for n-type doping, which was 1.43 at 660 K for Li2BeAl and 0.39 at 1000 K for Li2BeGa alloy. The high values of ZT especially for electron-dopped Li2BeAl suggest the great potential of this material for use in thermoelectric devices. This study suggests that the proposed materials have potential applications in spintronic devices and thermoelectric materials due to their intermetallic character and effective thermoelectric coefficients.

Electronic interfacial thermal conductance between metal nano-films in sub-picosecond non-equilibrium transport process

Interfaces play a critical role in nanoscale thermal transport, and understanding thermal transport mechanisms across metal/metal interfaces at the non-equilibrium states is urgently needed for highly integrated electronic structures or devices. In this work, the electronic interfacial thermal conductance hee of two metal interfaces, Au/Pt and Au/Al, was measured by time domain thermoreflectance (TDTR) at the non-equilibrium states and an extended two-temperature model was applied to well describe the interactions of electrons between the metal films. For the Au/Pt structure, the measured hee is 4.4 ± 1.8 GWm−2K−1, which is consistent with the predicted value by the electronic diffuse mismatch model (DMM). While for the Au/Al structure, the measured hee (0.13±0.05 GWm−2K−1) is an order of magnitude smaller than that of Au/Pt and the predicted value of the electronic DMM. The results indicate that even the extremely thin oxide layer at the Au/Al interface can significantly hinder the electron thermal transport across the metal interface. Overall, our findings contribute to revealing the non-equilibrium interfacial thermal transport mechanisms and pave the way for designing the highly integrated electronic devices.

Thermal conductivity of epoxy resin films doped with a polythiophene/graphene complex or aluminum nitride

AbstractPolymer composites with thermal conductivity are attractive for heat dissipation in electronic devices. We prepared epoxy resin‐based composite films filled with polythiophene [poly(3‐hexylthiophene‐2,5‐diyl)] (P3HT)/graphene complex or aluminum nitride (AlN). The composite films were characterized by electron microscopic observation, thermogravimetric analysis, and thermal conductivity measurements. The addition of a small content of P3HT/graphene complex (<1 wt%) increased both the out‐of‐plane and in‐plane thermal conductivities of the epoxy resin. The addition of AlN also increased thermal conductivity, but ≥40 wt% was required to obtain thermal conductivity comparable with that of an epoxy resin film doped with 0.9 wt% P3HT/graphene complex. The present results illustrate the potential of P3HT/graphene complexes as fillers for improving the thermal conductivity of epoxy resins without affecting their insulating properties.Highlights Polythiophene/graphene fillers increased epoxy resin films' thermal conductivity. To raise the thermal conductivity of epoxy resin films high AlN content was needed. In‐plane/out‐of‐plane epoxy resin films' thermal conductivities were evaluated.

A Tape-Wrapping Strategy towards Electrochemical Fabrication of Water-Dispersible Graphene.

Graphene has achieved mass production via various preparative routes and demonstrated its uniqueness in many application fields for its intrinsically high electron mobility and thermal conductivity. However, graphene faces limitations in assembling macroscopic structures because of its hydrophobic property. Therefore, balancing high crystal quality and good aqueous dispersibility is of great importance in practical applications. Herein, we propose a tape-wrapping strategy to electrochemically fabricate water-dispersible graphene (w-Gr) with both excellent dispersibility (~4.5 mg/mL, stable over 2 months), and well-preserved crystalline structure. A large production rate (4.5 mg/min, six times faster than previous electrochemical methods), high yield (65.4% ≤5 atomic layers) and good processability are demonstrated. A mechanism investigation indicates that the rational design of anode configuration to ensure proper oxidation, deep exfoliation and unobstructed mass transfer is responsible for the high efficiency of this strategy. This simple yet efficient electrochemical method is expected to promote the scalable preparation and applications of graphene.

Wide-range thermal conductivity modulation based on protonated nickelate perovskite oxides

The perovskite oxides ReNiO3 (Re = rare-earth elements) are promising functional materials due to their strongly correlated electrons. Except for the well-known intrinsic metal-insulating transition in these materials, recent progresses have proved that protonation of ReNiO3 can bring about interesting Mott transition in this series. To date, in these protonated species (H-ReNiO3), huge resistance switching, fast ionic diffusion, and their applications as an iontronic transistor, memristor, and fuel cell are reported. In this work, the thermal conductivities of H-ReNiO3 (Re = La, Nd, Sm, and Eu) epitaxial thin films are investigated. The protonation-induced Mott transition can effectively modulate the electronic thermal conductivity while the lattice thermal conductance is less affected. Hence, at room temperature, the metallic LaNiO3 and NdNiO3 exhibit reversible wide thermal conductivity modulation, in ranges of 2.6–12.0 and 1.6–8.0 W m−1 K−1, respectively. These values are much larger than other thermal regulation materials based on transition metal oxides. Thus, our work reveals the great potential of ReNiO3 being applied as a thermal-regulating material. The fast ionic diffusion in H-ReNiO3 also guarantees that a fast response and wide-range thermal transistor can be realized by H-LaNiO3 and H-NdNiO3 in the future.

Thermoelectric optimization using first principles calculation and single parabolic band model: a case of Ca0.5La0.5−x Bi x MnO3 (x = 0, 0.25)

Conducting optimization calculations for thermoelectric performance can be beneficial in guiding the direction of further experimental work. In our study, we utilize a combination of the first principle, Boltzmann transport and restructured single parabolic band model to investigate the half-doped semiconductors based on manganite. Ca0.5La0.5−x Bi x MnO3 (x = 0, 0.25) as samples shows the power factor (PF) optimum value of 30% and 69% for x = 0 and 0.25, respectively at a temperature of 800 K. In addition, both samples show two to three orders of magnitude smaller lattice thermal conductivity than their electronic thermal conductivity. This excludes complex phononic transport mechanisms from the calculation of the figure of merit (ZT). The ZT calculations of Ca0.5L0.5MnO3 and Ca0.5L0.5−x Bi x MnO3 are corrected by the ratio of the transport relaxation time of electrical conductivity to the transport relaxation time of electronic thermal conductivity by the Lorenz number, resulting in ZT values of 0.063 and 0.327 at a temperature of 800 K, respectively.

Study of mechanical, optoelectronic, and thermoelectric properties of Rb2ScAuZ6 (Z = Br, I) for energy harvesting applications

In the current article, the structural, mechanical, optoelectronic, and thermoelectric properties of Rb2ScAuZ6 (Z = Br, I) have been predicted using the density functional theory (DFT) approach. The tolerance factor, phonopy, and formation energy analysis validated the structural, dynamic, and thermodynamic stability of Rb2ScAuBr6 and Rb2ScAuI6, respectively. Likewise, the investigated elastic properties concluded that both materials exhibit mechanical stability and possess ductile characteristics. The directional-dependent elastic moduli revealed the anisotropy features. The indirect bandgaps determined by TB-mBJ approximation are 2.1 eV and 1.6 eV for Rb2ScAuBr6 and Rb2ScAuI6, respectively. Optical absorption, reflectivity, refractive index, and dielectric constants have been assessed in the energy range between 0 and 6 eV to ensure efficient absorption in the visible spectrum. Both materials have appropriate optical parameters for utilization in photovoltaic systems. Further, using the BoltzTraP code, the thermoelectric properties have been calculated to evaluate the thermoelectric efficiency. Both perovskites have lower lattice and electronic thermal conductivity, a higher Seebeck coefficient, and a higher figure of merit, making them ideal candidates for thermoelectric applications.

Review of the second charged-particle transport coefficient code comparison workshop

We report the results of the second charged-particle transport coefficient code comparison workshop, which was held in Livermore, California on 24–27 July 2023. This workshop gathered theoretical, computational, and experimental scientists to assess the state of computational and experimental techniques for understanding charged-particle transport coefficients relevant to high-energy-density plasma science. Data for electronic and ionic transport coefficients, namely, the direct current electrical conductivity, electron thermal conductivity, ion shear viscosity, and ion thermal conductivity were computed and compared for multiple plasma conditions. Additional comparisons were carried out for electron–ion properties such as the electron–ion equilibration time and alpha particle stopping power. Overall, 39 participants submitted calculated results from 18 independent approaches, spanning methods from parameterized semi-empirical models to time-dependent density functional theory. In the cases studied here, we find significant differences—several orders of magnitude—between approaches, particularly at lower temperatures, and smaller differences—roughly a factor of five—among first-principles models. We investigate the origins of these differences through comparisons of underlying predictions of ionic and electronic structure. The results of this workshop help to identify plasma conditions where computationally inexpensive approaches are accurate, where computationally expensive models are required, and where experimental measurements will have high impact.

Loose bonding induced ultralow lattice thermal conductivity of a metallic crystal KNaRb

In the domain of metallic systems, electronic thermal conductivity typically governs heat transfer, while lattice (phononic) thermal conductivity (LTC) remains non-negligible magnitude. This study introduces the exceptional metallic material, cubic half-Heusler-type KNaRb, via phonon Boltzmann transport equation (BTE) resolution and first-principles calculations. KNaRb exhibits an ultralow LTC of 0.114 W/mK at room temperature, comparable to the lowest reported for metallic materials, contributing merely 0.66 % to overall thermal transport. Analysis attributes KNaRb's low LTC to low group velocity and strong anharmonicity, originating from its loosely bonded electronic structure. Acoustic modes, primarily from Rb atoms, dominate thermal transport. Examination of mean square displacement and potential energy profiles reveals significant movement of loosely bonded Rb atoms within KNaRb, acting as intrinsic "rattlers," inducing pronounced phonon anharmonicity and ultrashort lifetimes. This study advances understanding of heat conduction in metals, offering insights into materials with extremely low lattice thermal conductivity for potential future applications.

Thermophysical properties of equiatomic CrMnFeCoNi, CrFeCoNi, CrCoNi, and CrFeNi high- and medium-entropy alloys

High- and medium-entropy alloys have emerged as promising materials with significant potential for diverse technical applications. Notably, their use in the field of energy technology has attracted particular interest, where thermophysical properties play a pivotal role. In this context, this study aims to investigate the thermophysical properties, namely thermal expansion behavior, thermal diffusivity, specific heat capacity, thermal conductivity, and the electric resistivity of single-phase face-centered cubic alloys between 300K and 773K. In addition to thermal conductivity, the electric resistivity was measured. Based on the Wiedemann-Franz law, electronic and phononic contributions to the overall thermal conductivity were evaluated. Complementary insights into the electronic state of the investigated materials were obtained by electron spin resonance measurements, revealing the presence of short-range ordering in all alloys. The specific heat capacity is found to dominate the thermal conductivity. Furthermore, the study shows the decisive influence of chemical complexity on the thermophysical properties. Notably, the observed influences extend to the electronic thermal conductivity, pointing out the correlation between composition and heat transport properties. This comprehensive investigation provides a foundation for understanding and tailoring the thermophysical behavior of the studied alloys, offering valuable insights for their targeted deployment in advanced energy applications.

Thermoelectric properties of monolayer and bilayer di boron nitride (di BN)

Motivated by the diverse uses of 2D materials in the modern technologies, we explore the temperature dependent thermoelectric properties of monolayer and bilayer di boron nitride. These materials are not still synthesized therefore the formation energy for monolayer and binding energy for bilayer is computed indicating the thermodynamical stability of both systems. The monolayer has a moderate direct band gap of 1.71 eV, while the bilayer possesses a band gap of 0.99 eV. The Seebeck coefficient has no substantial thickness and directional dependency. The Seebeck coefficient for bilayer decreases more as compare to monolayer with increasing temperature and at 600 K it decreases more than 1.7 times as compared to monolayer. However, the bilayer system has a longer carrier relaxation time than the monolayer system. Besides, the p-type relaxation in the ZZ-direction is longer than the n-type for both monolayer and bilayer systems. Consequently, the electrical and electronic thermal conductivities are two times larger in bilayer system. Here, p-type doping system have higher magnitude of electrical and electronic thermal conductivities than n-type doping system. The bilayer system has a greater lattice thermal conductivity than the monolayer. As results, we obtain that the maximum ZT of 0.8 in the bilayer system while the monolayer has a maximum ZT of 0.36 at 600 K with hole doping.

A Density Functional Theory Exploration of Cs2B′B″I6 (B′B″: BeCa, BeSr, GeCd, GeBe, GeMg) Halide Double Perovskites for Optimal Solar Cell and Renewable Energy Applications

A comprehensive investigation into the structural, elastic, optoelectronic, and thermoelectric properties of Cs2B′B″I6 halide double perovskites (DPs), where B′B″ represents various combinations, including BeCa, BeSr, GeCd, GeBe, and GeMg, is conducted. Using the full‐potential linearized augmented plane wave approach within the density functional theory framework, this analysis confirms the materials’ structural and dynamic stabilities through negative formation energies and adherence to elastic constant stability criteria. The generalized gradient approximation and the modified Becke–Johnson (mBJ) potential for electronic structure calculations are utilized. Notably, Cs2B′B″I6 DPs with B′B″ as BeCa or BeSr exhibit direct bandgaps (Γ–Γ), while those with B′B″ as GeCd, GeBe, or GeMg display indirect bandgaps (X–L). These findings offer valuable insights into the potential use of these materials in photovoltaic and optoelectronic devices. Furthermore, the exploration of thermoelectric properties, covering electrical conductivity, Seebeck coefficient, electronic thermal conductivity, and figure of merit at temperatures of 300, 600, and 900 K, suggests that Cs2B′B″I6 DPs, regardless of the specific B′B″ composition (BeCa, BeSr, GeCd, GeBe, GeMg), holds promise for applications in thermoelectric devices.

Design, Construction and Programming of a Low-Cost Pulsed High-Voltage Direct Current Power Supply for the Electrophoretic Deposition of Silicon Carbide Mixed with Graphite and/or Alumina for Thermoelectric Applications

This document describes a proprietary design, construction, programming and testing of a low-cost pulsed high-voltage direct current (HVDC) power supply with an output of 430 V and power of 25 W. The design obtained allows costs to be reduced compared to commercial ones, highlighting that the manufacturing of this HVDC is easy to replicate. To demonstrate the operation of the pulsed power supply prototype, coatings of silicon carbide (SiC) and SiC mixed with graphite (C) and/or alumina (Al2O3) were made using the electrophoretic deposition (EPD) method. After processing, samples underwent a heat treatment at 500 °C to evaluate their thermoelectric (TE) efficiency. The samples were analysed via X-ray diffraction (XRD), scanning electron microscopy (SEM), Raman spectroscopy, Seebeck coefficient, electrical conductivity and thermal conductivity. The Seebeck coefficient, electrical conductivity and thermal conductivity were measured in a temperature range of 100–500 °C in a nitrogen (N2) atmosphere. The electrical conductivity of the SiC 6C-4Al sample was 0.65 S/cm at 500 °C, while the maximum Seebeck coefficient was 2500 μV/K of the SiC 6C-4Al sample at 200 °C. The thermal conductivity of SiC 6C-4Al was in the range of 0.35–0.37 W/m·K, which was much lower than the SiC sample free of alumina and graphite in the same measured temperature range. In conclusion, the SiC 6C-4Al sample presented the highest figure of merit with a ZT ≈ 0.01.

Enhancing thermoelectric performance of p-type SnTe through manipulating energy band structures and decreasing electronic thermal conductivity

Enhancing thermoelectric performance of p-type SnTe through manipulating energy band structures and decreasing electronic thermal conductivity

High Thermoelectric Performance in Bismuth Telluride via Constructing MoSe2-2D Heterojunction.

Currently, the only thermoelectric (TE) materials commercially available at room temperature are those based on bismuth telluride. However, their widespread application is limited due to their inferior thermoelectric and mechanical properties. In this study, a strategy of growing a rigid second phase of MoSe2 is employed, in situ within the matrix phase to achieve n-type bismuth telluride-based materials with exceptional mechanical and thermoelectric properties. The in situ grown second phase contributes to both the electronic and lattice thermal conductivities. This is primarily attributed to the strong energy filtering effect, as the second phase forms a semi-common lattice interfacial structure with the matrix phase during growth. Furthermore, for composites containing 2wt% MoSe2, a maximum zT value of 1.24 at 373K can be achieved. On this basis, 8-pair TE module is fabricated and 1-pair TE module is optimized using a homemade p-type material. The optimized 1-pair TE module generates a maximum output power of 13.6µW, which is twice that of the 8-pair TE module and four times more than the 8-pair TE module fabricated by commercial material. This work facilitates the development of the TE module by presenting a novel approach to obtaining bismuth telluride-based thermoelectric materials with superior thermoelectric and mechanical properties.

DFT study of the half‐metallic variant perovskites A2OsX6 (A = Rb/Cs; X = Cl/Br) for spintronic and thermoelectric applications

AbstractWe present our results of the spin‐polarized calculations on the structural, magneto‐electronic, thermodynamic, and thermoelectric properties of vacancy‐ordered double perovskites A2OsX6 (A = Rb/Cs; X = Cl/Br). We utilized the Wu‐Cohen generalized gradient approximation (Wu‐GGA) and the mBJ scheme to determine a more reliable electronic structure. The compounds exhibit negative formation energy, suitable tolerance factor, and a stable phonon spectrum, indicating their stability. The compounds show half‐metallicity, acting as semiconductors with direct band gaps between 2 and 3 eV in the spin‐up orientation while metallic in the spin‐down. Each compound shows a total spin magnetic moment of 2.00 μB per formula unit, with Os‐t2g states contributing the most (~1.5 μB). The computed thermoelectric coefficient indicates the usability of these compounds across a wide temperature range (200–800 K) with high electrical conductivity and low electronic thermal conductivity. The compounds exhibit high Seebeck coefficient and figure of merit (ZT), making them suitable for thermoelectric applications. With ferromagnetic and half‐metallic characteristics, these compounds could be promising candidates for spintronics, thermoelectronic, and data storage applications.

Validation of the Wiedemann-Franz Law in Solid and Molten Tungsten above 2000K through Thermal Conductivity Measurements via Steady-State Temperature Differential Radiometry.

We measure the thermal conductivity of solid and molten tungsten using steady state temperature differential radiometry. We demonstrate that the thermal conductivity can be well described by application of Wiedemann-Franz law to electrical resistivity data, thus suggesting the validity of Wiedemann-Franz law to capture the electronic thermal conductivity of metals in their molten phase. We further support this conclusion using abinitio molecular dynamics simulations with a machine-learned potential. Our results show that at these high temperatures, the vibrational contribution to thermal conductivity is negligible compared to the electronic component.

Electronic, Mechanical, and thermoelectric properties of Ge/Zn co-doped SnSe: first-principles calculations

Materials based on tin selenide have attracted significant attention due to their unique properties, particularly their high ZT value. This study investigates the impact of co-doping Germanium and Zinc on the electronic, mechanical, and thermoelectric properties of SnSe crystal using first-principles calculations. The doped structure demonstrated a p-type semiconducting behavior with a triclinic stable structure, which was predicted by the calculated elastic constants. Thermoelectric properties were studied for both doped and undoped systems across a wide range of carrier concentrations and temperatures. Results showed that co-doping SnSe with Ge/Zn reduced electronic thermal conductivity at room temperature while simultaneously doubling the Seebeck coefficient. This promising combination of features suggests high thermoelectric performance for the material.

Progress of open systems at Budker Institute of Nuclear Physics

This paper is based on a report at the 2nd International Fusion Plasma Conference & 13th International Conference on Open Magnetic Systems for Plasma Confinement (iFPC & OS 2023), August 21–25, 2023, Busan, Korea and provides a brief overview of the status of work at the Budker Institute on the study of hot plasma confinement in open-type magnetic traps with a linear axisymmetric configuration. The main attention is paid to key problems: magnetohydrodynamics (MHD) stability in regimes with extremely high relative pressure, longitudinal electronic thermal conductivity, stability with respect to the development of kinetic modes and transverse transport. This paper provides an overview of the methods we are developing to address these problems, the experimental and theoretical results achieved and plans for future development. The last section of the article provides brief information about the preliminary design of the gas-dynamic multiple-mirror trap device, the development of which has been completed.

Strain induced modulations in the thermoelectric properties of 2D SiH and GeH monolayers: insights from first-principle calculations

The present paper is primarily focused to understand the strain driven alterations in thermoelectric (TE) properties of two-dimensional SiH and GeH monolayers from first-principle calculations. Electronic band structures and the associated TE properties of the compounds under ambient and external strains have been critically unveiled in terms of Seebeck coefficients, electrical conductivities, power factors and electronic thermal conductivities. The phonon dispersion relations have also been investigated to estimate the lattice thermal conductivities of the systems. The TE figure of merits of SiH and GeH monolayers under ambient and external strains have been explored from the collective effects of their Seebeck coefficients, electrical conductivities, electronic and lattice thermal conductivities. The present study will be helpful in exploring the strain induced TE responses of SiH and GeH compounds which in turn may bear potential applications in clean and global energy conservation.