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Enhancement of thermoelectric properties at room temperature has been recently demonstrated by spark plasma sintered PbTe nanocubes as compared to other PbTe nanostructures as well as Bulk material. The Seebeck coefficient has been reported to be 400 µV/K which is much higher than the bulk. Moreover, a moderate electrical conductivity ∼ 8000 S/m at room temperature results in considerable higher value of power factor S2σ ∼ 1.28 x 10-3 Wm-1K-2. The enhanced thermoelectric properties have been conjectured to be present due to energy filtering effects at numerous interfaces introduced by nanostructuring. We study how the interfacial scattering affects the power factor by performing theoretical modelling based on Boltzmann Transport Equation (BTE). We also investigate in detail, the role of various electronic parameters such as size, shape, mobility and effective mass etc., on interfacial scattering to optimize its effect on power factor.
We synthesized twin-mesogen epoxy polymer in which there were two 2,7-naphthalene benzoate as mesogens connected by four carbons alkyl chain and investigated the effects of higher-order structure changes due to the differences of alkyl chain length and mesogen groups on thermal conductivities. This polymer is abbreviated as TME2,7-NB4. NB means naphthalene benzoate and 4 means spacing carbon number. As a result, the thermal conductivity of TME2,7-NB4 was higher than that of TME2,7-NB8, but the coherent length D was less than that of TME2,7-NB8.
This paper reports the effect of Ar molar flow-rate on thermodynamic efficiency analysis of zinc oxide-zinc sulfate (ZnS-ZnO) water splitting cycle useful for solar H2 production. The thermodynamic efficiency analysis is conducted using the HSC Chemistry 7.1 software and its thermodynamic database. Influence of Ar molar flow-rate on total solar energy input essential for the continuous operation of the cycle is explored. Furthermore, the solar-to-fuel energy conversion efficiency for the ZnS-ZnO water splitting cycle is determined.
A solar thermoelectric generator (STEG) system composed of an optical concentrator system (OPS), a Bismuth Telluride thermoelectric module (TEG), and a cold plate-based cooling system (CPCS) was numerically simulated, to measure the efficiency of electric generation of a commercial thermoelectric module under controlled temperatures. The OPS is composed by a Fresnel lens that allows a temperature of around 200 °C, the OPS works with a solar irradiance of 1000 W/m2 (AM 1.5 Reference) and an optical concentration of 60. The OPS is coupled to the hot side of the TEG that consists of a commercially available thermoelectric module. The CPCS maintains a temperature of around 50 °C on the cold side of the TEG. To evaluate the configuration, a computational fluid dynamic (CFD) analysis was carried out to evaluated the thermal performance of the CPCS and the temperature achieved on the upper surface of the cooling device. Based on the numerical results generated by the CFD analysis, an analytical TEG efficiency of around 5% was achieved when a temperature difference, between the hot and cold sides of the commercial TE module, of 150 °C was maintained. We perform an analysis using the Hogan and Shih model that uses the thermoelectric material properties exposed by Chen et al.
A method for controlling the conduction-type in Mg2Si films without doping is investigated. Mg2Si films exhibit p-type conduction after a post-heat treatment up to 500 °C in atmospheric He. However, covering the films with Mg ribbon during a subsequent heat treatment at 500 °C converts the conduction to n-type, demonstrating that the heat treatment atmosphere can control the conduction type. Based on the reported first principles calculations suggesting that interstitial Mg and Mg vacancies in Mg2Si are the origins of n-type and p-type conduction, respectively, the post-heat treatment in He induces Mg vacancies due to the evaporation of Mg from the film, resulting in p-type conduction. The subsequent heat treatment when the film is covered with Mg ribbon fills the Mg vacancies and the additional interstitial Mg is incorporated, resulting in n-type conduction. These observations differ from the reported data for heat treatment of stable n-type conduction in non-doped Mg2Si-sintered bodies and may realize a novel control method for the conduction type in Mg2Si films.
We applied NiSi2 as an electrode for thermoelectric modules because NiSi2 has high electric conductivity and is expected to suppress the inter-diffusion of Si from MgSi2 and higher manganese silicide (HMS). The thermal expansion coefficient of NiSi2 is close to that of Mg2Si but differs from that of HMS. Therefore, to reduce thermal stress, we tried to insert a buffer layer consisting of HMS and NiSi2 for the interface between the HMS sintered body and the NiSi2 electrode. The NiSi2 was prepared by using spark plasma sintering (SPS) equipment. NiSi2 electrodes and gradients were formed and connected with the HMS by SPS treatment. Crack-free bonding was achieved by inserting gradients consisting of HMS and NiSi2. The inserted composite buffer layer reduced interface stress and interface resistance between HMS and NiSi2.
Cr-doped higher manganese silicides (HMSs) (Mn1-xCrx)Si1.75 (x = 0–0.35) have been prepared by repeated sintering from raw elemental powder using spark plasma sintering. The a- and cMn-axis length increases with increasing Cr content x. The results of powder X-ray diffraction and microstructural observation suggest that impurity phases, e.g. (Mn, Cr)Si and CrSi2, exist in the samples with x = 0.20 or above. The electrical resistivities and Seebeck coefficient decrease with increasing Cr content x. The Cr content x of 0.10 indicated the largest power factor at 850 K (1.39×10-3W/mK), followed in order by x of 0.25, 0, 0.05, 0.15, 0.20. To confirm the effect of Cr-doping on outputs of modules, two paired p-n modules consisting of n-type purchased Mg2Si and p-type Cr-doped HMS with x = 0, 0.05, 0.10, and 0.20 elements were prepared. The module consisting of (Mn0.9Cr0.1)Si1.75 showed the highest output, that is, 845 mW at 873 K on the hot side. There was approximately 8% improvement compared with that of the module consisting of Cr-free elements.
Microwave synthesis of Copper Zinc Tin Sulphide (CZTS) sphere like particles has been demonstrated. The structural and morphological properties of CZTS particles are characterized by XRD, SEM and Raman spectroscopy and subsequently thermoelectric properties are investigated. XRD results of prepared powder sample matches well with tetragonal crystal structure of CZTS bulk. No other impurity phase has been detected from the XRD analysis. Raman spectrum further confirms the formation of single phase CZTS with characteristics peak for CZTS at 334.1 cm-1. SEM studies reveal that the CZTS particles are spherical in shape with uniform sizes of ∼ 250-350 nm. Hot pressed CZTS system shows a power factor ∼21 µW/mK2 and ZT∼ 0.024 at 623 K. Significant enhancement in the Figure of merit for CZTS system is observed in comparison to reported nanostructures of the same system may be due to increased electrical conductivity.