High Electron Thermal Conductivity Research Articles

The growth evolution of SnSe-doped SnTe alloy by in-situ selenization substitution method

In the era of increasing environmental pollution and energy crisis, the development of thermoelectric materials to achieve the reuse of waste heat energy is of great significance. SnTe, as an environmentally friendly thermoelectric material, its high electronic-thermal conductivity and coupled high electrical conductivity originated from intrinsic high carrier hole concentration leads to the unsatisfactory thermoelectric properties. With a lot of research going on to optimize thermoelectric performance by decoupling the thermo-electrical contradiction, the entropy engineering strategy, which can independently modulate lattice thermal conductivity is proved to be feasible by increasing the internal configurational entropy through doping. However, due to the uncontrollable growth microscopic process and the perturbation of film quality, the desired precise phase doping remains a challenge. In this work, we report an instantiation of the entropy increase of SnSe-doped SnTe alloy thin films prepared by two-step magnetron sputtering and selenization method. The microstructure and physical properties of thin films were investigated for replaying and controlling the growth evolution of in-situ selenization substitution. When the reaction temperature and duration were adjusted to 300℃ and 30 mins respectively, the desired pure phase doping was obtained. This work provides a new method of doping modification of SnTe materials, and the product as a new functional material expands the thermoelectric material library. In particular, it has positive reference significance for the development of synthesis controllability and structure establishment of complex polycrystalline materials.

Thermoelectric Properties Investigation of Ni/Co Doped ZrCoBi Half-Heusler Alloy

Half-Heusler (HH) thermoelectric (TE) composites have been extensively inspected due to their excellent TE properties in the medium- to high-temperature range. First-principle calculations make it easier to discover or improve more HH compounds. This article presents an ab initio theoretical evaluation of TE properties of Half-Heusler alloy, when doped with Nickel (Ni), using FP-LAPW and the semi classic Boltzmann theory. Thermoelectric parameters were calculated using BoltzTraP code, like Seebeck coefficient ( ), electrical conductivity to relaxation time ratio ( ), electronic thermal conductivity to relaxation time ratio ( ), thermoelectric power factor to relaxation time ratio ( ), and the dimensionless figure-of-merit ( ) in a temperature range of . Calculated Seebeck coefficient reveals that the studied alloys show a tendency to conduct as p-type with balanced TE performance between both charge carriers (holes and electrons). A high electronic thermal conductivity value is found, which predicts a potential use in heat sink applications for the investigated alloys. Obtained results, such as a high thermoelectric power factor and , postulate that alloys could have potential thermoelectric applications.

High thermoelectric performance of Co-doped Cu2SnS3-attapulgite nano-composites achieved by synergetic manipulation of electrical and thermal transport properties

Mohite-type Cu2SnS3 has merged as a promising environmentally-friendly thermoelectric candidate. When heavily hole-doped, it exhibits a large power factor (PF) by virtue of a high electrical conductivity (σ), which results in an undesired high electronic thermal conductivity (κe) that limits the ZT value. In the present work, nanocomposites of Co-doped Cu2Sn0.8Co0.2S3 embedded with fibrous in-situ-dehydrated attapulgite (D-ATT) nanorods are prepared, and the effect of D-ATT on the thermoelectric properties are investigated. Results show that, with the incorporation of D-ATT, σ is lowered effectively as expected as a primary result of charge compensation caused by a donor effect of D-ATT, which gives rise to an optimal reduction of κe by 50% in the studied temperature range, accompanied with an enhanced Seebeck coefficient (S) and high PFs maintained at ~9.4 μW cm−1 K−2 at 773 K. Meanwhile, the lattice thermal conductivity is strongly suppressed due to the intensified phonon scattering with ATT addition, leading to an ultralow value of 0.27 W m−1 K−1 at 773 K. Finally, a maximal ZT of ~1.0 has been achieved in the sample with 0.2 wt% D-ATT at 773 K, which stands a new record for Cu2SnS3-based TE materials.

Enhanced thermoelectric performance in polymorphic heavily Co-doped Cu2SnS3 through carrier compensation by Sb substitution

ABSTRACT Heavily acceptor-doped Cu2SnS3 (CTS) shows promisingly large power factor (PF) due to its rather high electrical conductivity (σ) which causes a modest ZT with a high electronic thermal conductivity (κe ). In the present work, a strategy of carrier compensation through Sb-doping at the Sn site in Cu2Sn0.8Co0.2S3 was investigated, aiming at tailoring electrical and phonon transport properties simultaneously. Rietveld analysis suggested a complex polymorphic microstructure in which the cation-(semi)ordered tetragonal phase becomes dominant over the coherently bonded cation-disordered cubic phase, as is preliminarily revealed using TEM observation, upon Sb-doping and Sb would substitute Sn preferentially in the tetragonal structure. With increasing content of Sb, the σ was lowered and the Seebeck coefficient (S) was enhanced effectively, which gave rise to high PFs maintained at ~10.4 μWcm−1K−2 at 773 K together with an optimal reduction in κe by 60–70% in the whole temperature range. The lattice thermal conductivity was effectively suppressed from 1.75 Wm−1K−1 to ~1.2 Wm−1K−1 at 323 K while maintained very low at 0.3–0.4 Wm−1K−1 at 773 K. As a result, a peak ZT of ~0.88 at 773 K has been achieved for Cu2Sn0.74Sb0.06Co0.2S3, which stands among the tops so far of the CTS-based diamond-like ternary sulfides. These findings demonstrate that polymorphic microstructures with cation-disordered interfaces as an approach to achieve effective phonon-blocking and low lattice thermal conductivity, of which further crystal chemistry, microstructural and electrical tailoring are possible by appropriate doping.

High temperature–high pressure phase transformation of Cu

DFT calculations (typically done at 0 K), Helmholtz free energy and Gibbs free energy calculations (for high temperature) within the quasi-harmonic approximation have been done in this manuscript to probe a metastable phase of Cu observed at high temperature and high pressure. The high electronic thermal conductivity observed for this new metastable phase of Cu may be beneficial for high temperature engineering applications in electronic and spacecraft device designs.

Tin Acceptor Doping Enhanced Thermoelectric Performance of n-Type Yb Single-Filled Skutterudites via Reduced Electronic Thermal Conductivity.

Although introducing more fillers in nanocages is beneficial to gain low lattice thermal conductivity within filling fraction limit, accompanying high electronic thermal conductivity usually results in an unsatisfactory figure of merit ZT in CoSb3. In this work, Sn is adopted to tailor the electronic transport behavior for a high-filled Yb0.3Co4Sb12 alloy through rapid melt spinning combined with hot-press sintering processes. In spite of the reduced electrical conductivity, the power factors are scarcely influenced due to improved Seebeck coefficients by the reduced carrier concentration and moderate ionized impurity scattering. However, the lower total thermal conductivity is synergistically tuned by the effective suppression of electronic thermal conductivity and the low lattice thermal conductivity. As a result, both the high maximum ZT value of 1.4 at 823 K and the average ZT value of ∼0.98 between 300 and 850 K can be achieved in the Yb0.3Co4Sb11.85Sn0.15 sample. This work illustrates a promising approach for improving thermoelectric properties by largely tuning the electronic thermal conductivity.

Anomalously high electronic thermal conductivity and Lorenz ratio in Bi2Te3 nanoribbons far from the bipolar condition

The Lorenz number (L) of a conductor is the ratio between its electronic thermal conductivity and electrical conductivity. It takes the Sommerfeld value of L0=π2/3kB/e2 in simple, metallically electronic systems where charge and heat are both carried by the same group of quasi-particles that experience elastic scattering. Higher values of L than L0 are possible in semiconductors where both electrons and holes co-exist at high densities, that is, in bipolar conduction. As a narrow-bandgap semiconductor, Bi2Te3 exhibits L > L0 which has been generally attributed to such bipolar conduction mechanisms. However, in this work, we report that L > L0 is still observed in individual, single-crystal Bi2Te3 nanoribbons even at low temperatures and when degenerately doped, that is, far from the bipolar conduction condition. This discovery calls for different mechanisms to explain the unconventional electronic thermal transport behavior in Bi2Te3.

Heating of a metal nanofilm during femtosecond laser pulse absorption

We have studied the temperature evolution of electrons and the lattice of a metal nanofilm interacting with a femtosecond s- or p-polarised pulse. It is shown that even if the film thickness is greater than the skin-layer depth, the temperature distribution during the pulse action may be close to the uniform one because of the high electron thermal conductivity, which leads to a rapid redistribution of energy over the film thickness.

An energy-conserving two-temperature model of radiation damage in single-component and binary Lennard-Jones crystals

Two-temperature models are used to represent the interaction between atoms and free electrons during thermal transients such as radiation damage, laser heating, and cascade simulations. In this paper, we introduce an energy-conserving version of an inhomogeneous finite reservoir two-temperature model using a Langevin thermostat to communicate energy between the electronic and atomic subsystems. This energy-conserving modification allows the inhomogeneous two-temperature model to be used for longer and larger simulations and simulations of small energy phenomena, without introducing nonphysical energy fluctuations that may affect simulation results. We test this model on the annealing of Frenkel defects. We find that Frenkel defect annealing is largely indifferent to the electronic subsystem, unless the electronic subsystem is very tightly coupled to the atomic subsystem. We also consider radiation damage due to local deposition of heat in two idealized systems. We first consider radiation damage in a large face-centered-cubic Lennard-Jones (LJ) single-component crystal that readily recrystallizes. Second, we consider radiation damage in a large binary glass-forming LJ crystal that retains permanent damage. We find that the electronic subsystem parameters can influence the way heat is transported through the system and have a significant impact on the number of defects after the heat deposition event. We also find that the two idealized systems have different responses to the electronic subsystem. The single-component LJ system anneals most rapidly with an intermediate electron-ion coupling and a high electronic thermal conductivity. If sufficiently damaged, the binary glass-forming LJ system retains the least permanent damage with both a high electron-ion coupling and a high electronic thermal conductivity. In general, we find that the presence of an electronic gas can affect short and long term material annealing.

Comparison between fluid electron-temperature-gradient driven simulations and Tore Supra experiments on electron heat transport

Abstract.In recent years, much attention has been devoted to the electron-temperature-gradient (ETG) driven instability as a possible explanation for the high electron thermal conductivity found in most tokamaks. The present contribution assesses whether a specific three-dimensional fluid ETG model can reproduce the conductivity observed in the Tore Supra tokamak [Equipe Tore Supra (presented by R. Aymar) 1989 Plasma Physics and Controlled Nuclear Fusion Research (Proc. 12th Int. Conf., Nice, 1988, Vol. 1.) Vienna: IAEA, p. 9]. Although the model reproduces fairly well the observed critical gradient, a large discrepancy factor, of the order of 50, is found for the ratio between the experimental and the simulated conductivity. On the basis of this study, one must conclude that the electron heat transport cannot be explained only with a fluid ETG turbulence model.

Temperature dependence of the thermal conductivity in chiral carbon nanotubes

The thermal conductivity of a chiral carbon nanotube (CCNT) is calculated using a tractable analytical approach. This is based on solving the Boltzmann kinetic equation with energy dispersion relation obtained in the tight binding approximation. The results obtained are numerically analysed. Unusually high electron thermal conductivity χ e z is observed along the tubular axis. The dependence of χ e z against temperature T was plotted for varying Δ z and a given Δ s ( Δ z and Δ s are the overlapping integrals (exchange energy) for the jumps along the tubular axis and the base helix, respectively). It is noted that χ e z shows a peaking behaviour before falling off at higher temperature. As Δ z varies from 0.010 eV to 0.048 eV for a given Δ s = 0.0150 eV , the peak values of χ e z shift from 40 000 W / m K at 100 K to 55 000 W / m K at about 300 K. Interestingly our results at 104 K which is 41 000 W / m K and occurred at Δ z = 0.023 eV compares very well with that reported for a 99.9% isotopically enriched 12C diamond crystal. Another interesting result obtained is the fact that the circumferential electron thermal conductivity χ e c appears to be very small. The ratio of χ e z to χ e c is of the order of 2.