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Electronic and Vibrational Properties of TiS <sub/>2</sub> , ZrS <sub/>2</sub> , and HfS <sub/>2</sub> : Periodic Trends Studied by Dispersion-Corrected Hybrid Density Functional Methods
摘要： The electronic and vibrational properties of TiS2, ZrS2, and HfS2 have been studied using dispersion corrected hybrid density functional methods. The periodic trends in electronic band structures, electronic transport coefficients, IR and Raman spectra, and phonon dispersion relations were investigated. Comparison to the available experimental data shows that the applied DFT methodology is suitable for the investigation of the layered transition metal dichalcogenide materials with weak interlayer Van der Waals interactions. The choice of damping function in the D3 dispersion correction proved to have surprisingly large effect. Systematic investigation of the periodic trends within group 4 disulfides reveals that TiS2 shows many differences to ZrS2 and HfS2 due to the more covalent M–S bonding in TiS2. ZrS2 and HfS2 mainly show differences for properties where the atomic mass plays a role. All three compounds show similar Seebeck coefficients, but clear differences in the relative electrical conductivity of cross- and in-plane directions. The transport and vibrational properties of thin TiS2 single crystals were also investigated experimentally.
关键词： ZrS2,HfS2,dispersion corrected hybrid density functional methods,thermoelectric properties,periodic trends,vibrational properties,electronic properties,TiS2
更新于2025-09-23 15:21:01
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Effect of DFT methods on electronic structure and <i>K</i> -absorption spectra of InPS <sub/>4</sub> : detailed studies of the optical, thermoelectric and elastic properties
摘要： The effect of exchange-correlation potential on InPS4 electronic structure was studied by applying GGA, GGA+U, mBJ, and mBJ+U potentials in the Kohn–Sham framework. The use of mBJ+U in full potential APW+lo method results in reliable K-absorption spectrum, which consists of nearly full experimental peaks of right intensity. The remarkable discrepancy between 1e w^( ) and 1e w?( ) occurs at 0 eV, 4 eV, 6 eV, and 9.5 eV, indicating the strong anisotropic optical properties of InPS4 at these energy levels. At 4 eV, the optical absorption of InPS4 has high order of 105cm?1 magnitude for wide energy range, at least within 4–20 eV. The figure of merit ZT achieves its highest value of about 0.8–1. InPS4 is a p-type semiconductor for chemical potential μ ranging from 0 eV to about 1.6 eV, but it is an n-type semiconductor for μ of about 1.6–2.7 eV. The Poisson’s ratio is equal to 0.26 and B/G@1.75. Indium thiophosphate InPS4 possesses rather low deformation resistance with the Young and shear moduli of 38.47 GPa and 15.27 GPa, respectively.
关键词： thermoelectric properties,elastic properties,optical properties,ab initio calculations,x-ray spectrum
更新于2025-09-23 15:19:57
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HBN-Encapsulated, Graphene-based, Room-temperature Terahertz Receivers, with High Speed and Low Noise
摘要： Uncooled terahertz photodetectors (PDs) showing fast (ps) response and high sensitivity (noise equivalent power (NEP) < nW/Hz1/2) over a broad (0.5?10 THz) frequency range are needed for applications in high-resolution spectroscopy (relative accuracy ～10?11), metrology, quantum information, security, imaging, optical communications. However, present terahertz receivers cannot provide the required balance between sensitivity, speed, operation temperature, and frequency range. Here, we demonstrate uncooled terahertz PDs combining the low (～2000 kB μm?2) electronic specific heat of high mobility (>50 000 cm2 V?1 s?1) hexagonal boron nitride-encapsulated graphene, with asymmetric field enhancement produced by a bow-tie antenna, resonating at 3 THz. This produces a strong photo-thermoelectric conversion, which simultaneously leads to a combination of high sensitivity (NEP ≤ 160 pW Hz?1/2), fast response time (≤3.3 ns), and a 4 orders of magnitude dynamic range, making our devices the fastest, broad-band, low-noise, room-temperature terahertz PD, to date.
关键词： terahertz,thermoelectric effect,graphene,photodetector
更新于2025-09-23 15:19:57
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Performance Evaluation of Unconcentrated Photovoltaic-Thermoelectric Generator Hybrid System under Tropical Climate
摘要： Indoor farming is among the approaches which can be adapted to improve agricultural sustainability and ensure the food security of countries. However, adopting indoor farming requires a high amount of energy to sustain the system. Incorporating a renewable energy system for supplying power to agricultural activities will allow the system to be more sustainable in the long run. An unconcentrated photovoltaic-thermoelectric generator (PV-TEG) hybrid system is designed based on the load requirement of an indoor farm. The hybrid system performance under Malaysia’s weather conditions was investigated and analyzed over three months. The designed system has shown its ability to provide sufficient power to the load, as well as supporting an additional load. Besides that, the TEGs power output was found to be dependent on the temperature as well as the types of connections used, where a higher temperature difference and series connection exhibited a better power output. Overall, the combination of the system showed that the addition of a TEG affects the efficiency and power output as compared to a standalone PV. Therefore, this implies that the hybrid system is able to exhibit a more positive outcome in certain weather conditions than a PV standalone system.
关键词： photovoltaic,sustainable agriculture,PV-TEG,indoor farming,thermoelectric generator
更新于2025-09-23 15:19:57
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A numerical study on a photovoltaic thermal system integrated with a thermoelectric generator module
摘要： In this work, a three-dimensional numerical model is developed to investigate the performance of a photovoltaic thermal system integrated with a thermoelectric generator module (PVT/TE). Furthermore, the effects of various operating parameters such as solar radiation, coolant mass flow rate, and inlet and ambient temperatures on the performance of both the PVT and PVT/TE systems are investigated and compared. Based on the obtained results, the electrical efficiency of the PVT/TE system, when exposed to solar radiation of 600 and 1000 W/m2, is 6.23% and 10.41% higher than that of the PVT system, respectively. Besides, the electrical efficiency of the PVT and PVT/TE by increasing the inlet fluid temperature from 26 oC to 34 oC, reduces by 2.58% and 4.56%, respectively. Furthermore, by increasing the ambient temperature from 26 oC to 34 oC, the electrical efficiency of the PVT reduces by 1.43%, the electrical efficiency of the PVT/TE increases by 0.82%. Based on the simulation results, the electrical efficiency of the PVT/TE system is much higher than that of the PVT system, while the PVT system benefits from higher thermal efficiency in comparison to the PVT/TE system.
关键词： Numerical simulation,Electrical efficiency,Thermal efficiency,Thermoelectric generator module (TE),Photovoltaic thermal system (PVT)
更新于2025-09-23 15:19:57
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Thermal management of high-power LED based on thermoelectric cooler and nanofluid-cooled microchannel heat sink
摘要： Effective thermal management for light-emitting diodes (LEDs) is critical, as temperature significantly affects their lifetime and performance. In this study, a system combining a thermoelectric cooler (TEC) and a microchannel heat sink (MHS) is investigated experimentally for thermal management of high-power LEDs. Nanofluids and water are used as coolant. The LED substrate temperature (Ts) is measured at various TEC powers, nanofluid concentrations, ambient temperatures of LED (Ta), and ambient temperatures of the fluid radiator (Ta,f). The effective thermal resistance (Rs-fa) of the LED substrate to the ambient of the fluid radiator is analyzed. Correlations of Ts and Rs-fa are obtained. Results show that the Ts is lowest when the TEC works at its rated power, and Ts is lower than Ta at Ta ≥ 55 °C. Using nanofluids instead of water as coolant reduces the Ts by up to 18.5 °C and decreases the thermal resistance by as much as 42.4%. The MHS heat transfer capacity is increased by 38.6%. The Ta,f exhibites greater influence on Ts compared to Ta. Results show that favorable performance of the thermal management of the high-power LED is obtained by the proposed nanofluid-cooled TEC-MHS system, particularly at high ambient temperature of LED.
关键词： Thermal management,Nanofluid,LED,Thermoelectric cooler,Thermal resistance,Microchannel heat sink
更新于2025-09-23 15:19:57
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Enhancement of Electrical Conduction and Phonon Scattering in Ga2O3(ZnO)9-In2O3(ZnO)9 Compounds by Modification of Interfaces at the Nanoscale
摘要： The Ga2O3(ZnO)9 and In2O3(ZnO)9 homologous phases have attracted attention as thermoelectric (TE) oxides due to their layered structures. Ga2O3(ZnO)9 exhibits low thermal conductivity, while In2O3(ZnO)9 possesses higher electrical conductivity. The TE properties of the solid solution of Ga2O3(ZnO)9-In2O3(ZnO)9 were explored and correlated with changes in the crystal structure. High-quality (1?x)Ga2O3(ZnO)9-xIn2O3(ZnO)9 (x = 0.0 to 1.0) ceramics were prepared by the solid-state route using B2O3 and Nd2O3 as additives. The crystal structures were analysed by x-ray diffraction, high-resolution transmission electron microscopy and atomic resolution scanning transmission electron microscopy–high-angle annular dark field imaging–energy dispersive x-ray spectroscopy (STEM–HAADF–EDS) techniques. A layered superstructure with compositional modulations was observed in all samples in the (1?x)Ga2O3(ZnO)9-xIn2O3(ZnO)9 system. All the ceramics exhibited nanoscale structural features identified as Ga- and In-rich inversion boundaries (IBs). Substitution of 20 mol.% In (x = 0.2) in the Ga2O3(ZnO)9 compounds generated basal and pyramidal indium IBs typically found in the In2O3(ZnO)m system. The (Ga0.8In0.2)2O3(ZnO)9 compound does not exhibit the structural features of the Cmcm Ga2O3(ZnO)9 compound, which is formed by a stacking of Ga-rich IBs along the pyramidal plane of the wurtzite ZnO, but features that resemble the crystal structure exhibited by the R3m In2O3(ZnO)m with basal and pyramidal indium IBs. The structural changes led to improved TE performance. For example, (Ga0.8In0.2)2O3(ZnO)9 showed a low thermal conductivity of 2 W/m K and a high power factor of 150 μW/m K2 giving a figure of merit (ZT) of 0.07 at 900 K. This is the highest ZT for Ga2O3(ZnO)9-based homologous compounds and is comparable with the highest ZT reported for In2O3(ZnO)9 homologous compounds.
关键词： thermoelectric,inversion boundaries,twin boundaries,ZnO,interfaces,homologous compounds
更新于2025-09-23 15:19:57
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Effect of Oxygen Partial Pressure on the Phase Stability of Copper–Iron Delafossites at Elevated Temperatures
摘要： Oxide-based materials are promising candidates for use in high temperature thermoelectric generators. While their thermoelectric performance is inferior to commonly used thermoelectrics, oxides are environmentally friendly and cost-effective. In this study, Cu-based delafossites (CuFeO2), a material class with promising thermoelectric properties at high temperatures, were investigated. This work focuses on the phase stability of CuFeO2 with respect to the temperature and the oxygen partial pressure. For this reason, classical material characterization methods, such as scanning electron microscopy, energy dispersive X-ray spectroscopy, and X-ray diffraction, were combined in order to elucidate the phase composition of delafossites at 900 ?C at various oxygen partial pressures. The experimentally obtained results are supported by the theoretical calculation of the Ellingham diagram of the copper–oxygen system. In addition, hot-stage X-ray diffraction and long-term annealing tests of CuFeO2 were performed in order to obtain a holistic review of the phase stability of delafossites at high temperatures and varying oxygen partial pressure. The results support the thermoelectric measurements in previous publications and provide a process window for the use of CuFeO2 in thermoelectric generators.
关键词： high temperature thermoelectric materials,delafossite,thermoelectric generator (TEG),phase stability,Ellingham diagram
更新于2025-09-19 17:15:36
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Thermoelectric Properties of (100) Oriented Silicon and Nickel Silicide Nanocomposite Films Grown on Si on Insulator and Si on Quartz Glass Substrates
摘要： We have grown (100) oriented composite films of Si and Ni silicide nanocrystals (Ni–Si NC film) on substrates of Si on insulator (SOI) and Si on quartz glass (SOQ). Owing to improvement of carrier transport properties and reduction of the thermal conductivity in the oriented films, they have higher dimensionless figures of merit, ZT of 0.22–0.42 for p-type Ni–Si NC film and 0.08–0.13 for n-type Ni–Si NC film than that of bulk Si (ZT < 0.01) at 30°C. The ZT values of p-type and n-type Ni–Si NC films were increased to 0.65 and 0.40 at 500°C, respectively.
关键词： silicon based thermoelectric materials,nanocomposite films,nickel silicide nanocrystals,silicon nanostructures,phonon scattering
更新于2025-09-19 17:15:36
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Heat and charge transport in bulk semiconductors with interstitial defects
摘要： Interstitial defects are inevitably present in doped semiconductors that enable modern-day electronic, optoelectronic, or thermoelectric technologies. Understanding the stability of interstitials and their bonding mechanisms in the silicon lattice was accomplished only recently with the advent of first-principles modeling techniques, supported by powerful experimental methods. However, much less attention has been paid to the effect of different naturally occurring interstitials on the thermal and electrical properties of silicon. In this work, we present a systematic study of the variability of heat and charge transport properties of bulk silicon, in the presence of randomly distributed interstitial defects (Si, Ge, C, and Li). We find through atomistic lattice dynamics and molecular dynamics studies that interstitial defects scatter heat-carrying phonons to suppress thermal transport—1.56% of randomly distributed Ge and Li interstitials reduce the thermal conductivity of silicon by ～30 and 34 times, respectively. Using first-principles density functional theory and semiclassical Boltzmann transport theory, we compute electronic transport coefficients of bulk Si with 1.56% neutral Ge, C, Si, and Li interstitials, in energetically favorable hexagonal, tetrahedral, split-interstitial, and bond-centered sites. We demonstrate that hexagonal-Si and hexagonal-Ge interstitials minimally impact charge transport. As an illustration of the relevance of this work for practical applications, we predict the thermoelectric property of an experimentally realizable bulk Si sample that contains Ge interstitials in different symmetry sites. Our research establishes a direct relationship between the variability of structures dictated by fabrication processes and heat and charge transport properties of silicon. The relationship provides guidance to accurately estimate performance of Si-based materials for various technological applications.
关键词： electronic transport,thermoelectric properties,interstitial defects,silicon,thermal conductivity
更新于2025-09-19 17:15:36