The thermoelectric effect enables direct and reversible conversion between thermal and electrical energy, and provides a viable route for power generation from waste heat. The efficiency of ...thermoelectric materials is dictated by the dimensionless figure of merit, ZT (where Z is the figure of merit and T is absolute temperature), which governs the Carnot efficiency for heat conversion. Enhancements above the generally high threshold value of 2.5 have important implications for commercial deployment, especially for compounds free of Pb and Te. Here we report an unprecedented ZT of 2.6 ± 0.3 at 923 K, realized in SnSe single crystals measured along the b axis of the room-temperature orthorhombic unit cell. This material also shows a high ZT of 2.3 ± 0.3 along the c axis but a significantly reduced ZT of 0.8 ± 0.2 along the a axis. We attribute the remarkably high ZT along the b axis to the intrinsically ultralow lattice thermal conductivity in SnSe. The layered structure of SnSe derives from a distorted rock-salt structure, and features anomalously high Grüneisen parameters, which reflect the anharmonic and anisotropic bonding. We attribute the exceptionally low lattice thermal conductivity (0.23 ± 0.03 W m(-1) K(-1) at 973 K) in SnSe to the anharmonicity. These findings highlight alternative strategies to nanostructuring for achieving high thermoelectric performance.
Thermoelectric materials offer an alternative opportunity to tackle the energy crisis and environmental problems by enabling the direct solid-state energy conversion. As a promising candidate with ...full potentials for the next generation thermoelectrics, tin selenide (SnSe) and its associated thermoelectric materials have been attracted extensive attentions due to their ultralow thermal conductivity and high electrical transport performance (power factor). To provide a thorough overview of recent advances in SnSe-based thermoelectric materials that have been revealed as promising thermoelectric materials since 2014, here, we first focus on the inherent relationship between the structural characteristics and the supreme thermoelectric performance of SnSe, including the thermodynamics, crystal structures, and electronic structures. The effects of phonon scattering, pressure or strain, and oxidation behavior on the thermoelectric performance of SnSe are discussed in detail. Besides, we summarize the current theoretical calculations to predict and understand the thermoelectric performance of SnSe, and provide a comprehensive summary on the current synthesis, characterization, and thermoelectric performance of both SnSe crystals and polycrystals, and their associated materials. In the end, we point out the controversies, challenges and strategies toward future enhancements of the SnSe thermoelectric materials.
Materials with ultrahigh or low thermal conductivity are desirable for many technological applications, such as thermal management of electronic and photonic devices, heat exchangers, energy ...converters and thermal insulation. Recent advances in simulation tools (first principles, the atomistic Green's function and molecular dynamics) and experimental techniques (pump-probe techniques and microfabricated platforms) have led to new insights on phonon transport and scattering in materials and the discovery of new thermal materials, and are enabling the engineering of phonons towards desired thermal properties. We review recent discoveries of both inorganic and organic materials with ultrahigh and low thermal conductivity, highlighting heat-conduction physics, strategies used to change thermal conductivity, and future directions to achieve extreme thermal conductivities in solid-state materials.
The enhancement of thermal conductivities of water in the presence of copper oxide and multiwalled carbon nanotubes is investigated for the first time. Hybrid nanofluid is a homogenous mixture of ...multiwalled carbon nanotubes-CuO particles suspended in water as the base fluid. The thermal conductivity of mixture is measured by KD2 Pro instrument. All thermal conductivity measurements are repeated three times in the range of 25–50 °C. A hot water bath is used to stabilize the temperature at 25, 30, 35, 40, 45 and 50 °C during the measurements. The results show that the thermal conductivity of the nanofluid increases at more solid concentration. Furthermore, the thermal conductivity of the nanofluid increases with the temperature; however, this increase is by far more noticeable in higher solid concentrations compared with the lower ones. Moreover, it is tried to propose a new correlation for predicting the thermal conductivity of the present nanofluid at different temperatures and volume fractions. The highest enhancement percentage was observed as 30.38% for the state of
T
= 50 °C and
φ
= 0.6%. However, the enhancement percentages were achieved as 25.57–30.38 for the state of
φ
= 0.6% at
T
= 25–50 °C, respectively.
From an environmental perspective, lead-free SnTe would be preferable for solid-state waste heat recovery if its thermoelectric figure-of-merit could be brought close to that of the lead-containing ...chalcogenides. In this work, we studied the thermoelectric properties of nanostructured SnTe with different dopants, and found indium-doped SnTe showed extraordinarily large Seebeck coefficients that cannot be explained properly by the conventional two-valence band model. We attributed this enhancement of Seebeck coefficients to resonant levels created by the indium impurities inside the valence band, supported by the first-principles simulations. This, together with the lower thermal conductivity resulting from the decreased grain size by ball milling and hot pressing, improved both the peak and average nondimensional figure-of-merit (ZT) significantly. A peak ZT of ∼1.1 was obtained in 0.25 atom % In-doped SnTe at about 873 K.
Comparison of the other models to new model and experimental data for 47nm nanoparticles 17 and different nanoparticles volume of fractions.
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•A dimensionless model is discussed to ...forecast thermal conductivity of nanofluids.•The proposed model considers knf, kbf, Φ, dp, Tnf, and t.•Proposed model has a good compatibility with experimental data of previous studies.
In this research, a dimensionless model is discussed to forecast effective thermal conductivity of nanofluids regarding the dimensionless groups. Nanofluids thermal conductivity is represented by this model as a function of thermal conductivity of nanoparticles and base liquid, nanoparticles size, volume fractions and interfacial shell properties. Moreover, temperature is considered as a most significant parameter for nanofluids thermal conductivity which influences even on the effective parameters. The results of modeling generate a non-linear correlation for thermal conductivity which demonstrates a good compatibility between present model and experimental data of Al2O3/H2O nanofluids compared to other models.
Polymer‐based thermal management materials (TIMs) show great potentials as TIMs due to their excellent properties, such as high insulation, easy processing, and good flexibility. However, the limited ...thermal conductivity seriously hinders their practical applications in high heat generation devices. Herein, highly transparent, insulating, and super‐flexible cellulose reinforced polyvinyl alcohol/nylon12 modified hexagonal boron nitride nanosheet (PVA/(CNC/PA‐BNNS)) films with quasi‐isotropic thermal conductivity are successfully fabricated through a vacuum filtration and subsequent self‐assembly process. A special structure composed of horizontal stacked hexagonal boron nitride nanosheets (h‐BNNSs) connected by their warping edges in longitudinal direction, which is strengthened by cellulose nanocrystals, is formed in PVA matrix during self‐assembly process. This special structure makes the PVA/(CNC/PA‐BNNS) films show excellent thermal conductivity with an in‐plane thermal conductivity of 14.21 W m−1 K−1 and a through‐plane thermal conductivity of 7.29 W m−1 K−1. Additionally, the thermal conductive anisotropic constants of the as‐obtained PVA/(CNC/PA‐BNNS) films are in the range of 1 to 4 when the h‐BNNS contents change from 0 to 60 wt%, exhibiting quasi‐isotropic thermal conductivity. More importantly, the PVA/(CNC/PA‐BNNS) films exhibit excellent transparency, super flexibility, outstanding mechanical strength, and electric insulation, making them very promising as TIMs for highly efficient heat dissipation of diverse electronic devices.
Quasi‐isotropically thermal conductive cellulose reinforced polyvinyl alcohol/nylon12 modified hexagonal boron nitride nanosheet films with high transparency, good electrical insulation, and super‐flexibility are successfully fabricated through a vacuum filtration and subsequent self‐assembly process. These films are very promising as thermal interface management materials for highly efficient heat dissipation of diverse electronic devices.
Polymer composites with super-high thermal conductivity have attracted many interests in aerospace and electrical fields. However, traditional polymer composites usually suffer from low thermal ...conductivity because of the high interfacial thermal resistance. Herein, by adopting a multi-dimensional filler composed of micro-silver (AgMP) and nano-silver (AgNP) particles, we prepare an epoxy/Ag composite with the maximum thermal conductivity of 58.3 W/m·K. Based on this, by introducing trace amount (0.12 vol%) of MXene, the thermal conductivity of the epoxy/Ag/MXene composite further increases to 72.7 W/m·K, which is 24.7% higher than that of Ag/Epoxy composites. Both of the super-high thermal conductivity enhancement in epoxy/Ag and epoxy/Ag/MXene composites should be attributed to the unique bridging effect of AgNP particles or MXene flakes. AgNP bridges AgMP via sintering while the MXene flakes bridge AgNP and/or AgMP by the strong interaction between MXene flakes and the Ag particles. The significant effect of the bridging between filler particles on the thermal conductivity of composites is elucidated and verified by FEM simulations. These findings provide new insights into the thermal transport in polymer-based composites and also suggest an approach to prepare polymer composites with super-high thermal conductivity.
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