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The quest for efficient thermoelectric materials has intensified with the advent of novel Janus monolayers exhibiting exceptional thermoelectric parameters. In this work, we comprehensively investigate the structural, electronic, transport, phonon, and thermoelectric properties of novel Janus γ -Pb 2 XY (X=S, Se; Y=Se, Te; X ≠ Y) monolayers using density functional theory combined with the Boltzmann transport equation. Our findings unveil the energetic, dynamic, thermal, and mechanical stability of these monolayers, along with their remarkable thermoelectric performance. Remarkably, the p-type γ -Pb 2 SeTe monolayer exhibits an outstanding figure of merit (ZT) of 6.88 at 800 K, attributed to its intrinsically low lattice thermal conductivity of 0.162 Wm - 1 K - 1 arising from strong phonon scattering, low group velocity, low phonon relaxation time, and a high Grüneisen parameter. Furthermore, these monolayers demonstrate high Seebeck coefficients and electrical conductivities, making them promising for efficient charge transport and thermoelectric energy conversion. Our results highlight the immense potential of Janus γ -Pb 2 XY monolayers as promising candidates for high-temperature thermoelectric applications and open up exciting avenues for further exploration of these novel two-dimensional materials in energy-related technologies. [ABSTRACT FROM AUTHOR]

The axial thermal conductance of a cylindrical cavity supporting the propagation of hybridized guided modes along its interface with SiO 2 is quantified and analyzed as a function of its radius and mean temperature. In contrast to the well-known radial thermal conductance, we show that the axial one increases with the cavity radius up to 1 cm, in which it takes its maximum that increases with temperature. A maximum thermal conductance of 289.4 nW·K−1 is found at 500 K, which is more than 3 orders of magnitude higher than the corresponding one found in the far-field regime. This top polariton thermal conductance along the cavity is comparable to the radiative one predicted by Planck's theory and thus represents a fundamental heat transport channel driven by hybridized guided modes able to amplify heat currents along a macroscale cylindrical cavity. [ABSTRACT FROM AUTHOR]

Bismuth telluride-based materials have been widely investigated due to their applications for the development of high-performance thermoelectric devices. Here, we numerically determine the effective electrical conductivity ( σ eff ), thermal conductivity ( k eff ), and Seebeck coefficient ( S eff ) of composite materials made up of VO 2 nanoparticles embedded in a Bi 0.5 Sb 1.5 Te 3 (BST) matrix. The temperature evolution of these three properties along with the thermoelectric figure of merit ( Z T = σ eff S eff 2 T / k eff ) is analyzed across the metal–insulator transition of VO 2 and for temperatures up to 550 K. For temperatures higher than 350 K, it is shown that VO 2 nanoparticles with a concentration of 34 % enhance the electrical conductivity and ZT of the matrix by about 16 % and 10 %, respectively, while the Seebeck coefficient remains pretty much constant. This indicates that VO 2 nanoparticles provide an effective way to enhance the thermoelectric efficiency of Bi 0.5 Sb 1.5 Te 3 materials. The calculated ZT values for VO 2 are in good agreement with the experimental data reported in the literature for temperatures higher than 350 K. The thermal conductivity values obtained for VO 2 in the insulating phase are in good agreement with the experimental data reported in the literature, which are used to calculate the interface thermal resistance between Bi 0.5 Sb 1.5 Te 3 and VO 2 . Furthermore, the ratio k eff / T σ eff is found to be higher than the Lorenz number for pure metals. Above the transition temperature of VO 2 (342.5 K), this ratio increases with temperature and concentration, allowing to evaluate the role of electrons as energy carriers in these systems. [ABSTRACT FROM AUTHOR]

Silicon carbide (SiC) aims to be the number one material for power microelectronics due to its remarkable thermal properties. Recent progress in SiC technology finally enabled the fabrication of crystalline SiC nanostructures. Yet, the thermal properties of SiC at the nanoscale remain overlooked. Here, we systematically study heat conduction in SiC nanostructures, including nanomembranes, nanowires, and phononic crystals. Our measurements show that the thermal conductivity of nanostructures is several times lower than that in bulk and that the values scale proportionally to the narrowest dimension of the structures. In the smallest nanostructures, the thermal conductivity reached 10% of that in bulk. To better understand nanoscale thermal transport in SiC, we also probed phonon mean free path and coherent heat conduction in the nanostructures. Our theoretical model links the observed suppression of heat conduction with the surface phonon scattering, which limits the phonon mean free path and thus reduces the thermal conductivity. This work uncovers thermal characteristics of SiC nanostructures and explains their origin, thus enabling realistic thermal engineering in SiC microelectronics.In this work, we systematically study heat conduction in SiC nanostructures, including nanomembranes, nanowires, and phononic crystals. Our measurements show that the thermal conductivity of nanostructures is several times lower than that in bulk and the values scale proportionally to the narrowest dimension of the structures. Additionally, we probed phonon mean free path and coherent heat conduction in these nanostructures. Our theoretical model links the observed suppression of heat conduction with the surface phonon scattering, which limits the phonon mean free path and thus reduces the thermal conductivity. [ABSTRACT FROM AUTHOR]

We theoretically and comparatively study the performance of spherical and cylindrical conductive thermal diodes operating with a phase-change material, whose thermal conductivity significantly changes in a narrow interval of temperatures. Simple analytical expressions are derived for the temperature profiles, heat flows and optimal rectification factors of both diodes. It is shown that the diode geometry has a strong impact on the temperatures and heat flows, but not so much on the diode rectification factor. Optimal rectification factors of 20.8% and 20.7% are obtained for the spherical and cylindrical diodes operating with a temperature difference of 376−300 = 76 K and 376.5-300 = 76.5 K between the terminals of VO2 and a phase invariant material, respectively. These similar rectification factors could be enhanced with a material thermal conductivity exhibiting a higher contrast than that of VO2. The obtained results can thus be useful to guide the development of phase-change materials able to optimize the rectification of conductive thermal diodes with different geometries. [ABSTRACT FROM AUTHOR]

Hysteresis loops exhibited by the thermophysical properties of VO2 thin films deposited on either a sapphire or silicon substrate have been experimentally measured using a high frequency photothermal radiometry technique. This is achieved by directly measuring the thermal diffusivity and thermal effusivity of the VO2 films during their heating and cooling across their phase transitions, along with the film-substrate interface thermal boundary resistance. These thermal properties are then used to determine the thermal conductivity and volumetric heat capacity of the VO2 films. A 2.5 enhancement of the VO2 thermal conductivity is observed during the heating process, while its volumetric heat capacity does not show major changes. This sizeable thermal conductivity variation is used to model the operation of a conductive thermal diode, which exhibits a rectification factor about 30% for small temperature differences (≈70 °C) on its terminals. The obtained results grasp thus new insights on the control of heat currents. [ABSTRACT FROM AUTHOR]