Papers by Keyword: Seebeck Coefficient

Abstract: Sr-doped CaMnO₃ materials have wide applications due to their thermal and electrical properties. The importance of the synthesis of Sr-doped CaMnO₃ material for various applications encourages researchers to evaluate and refine the synthesis process. In this study, Ca_1-xSr_xMnO₃ (x = 0; 0.05; 0.1; 0.15; 0.2) system has been prepared by sol-gel method followed by conventional sintering process at 850°C for 8 hr. A thorough discussion has been made on the outcomes derived from the investigation on the structural, electrical, and thermal properties of Sr-doped CaMnO₃ system using powder x-ray diffraction, scanning electron microscopy, energy dispersive spectroscopy, DC fourprobe method, thermal expansion studies, and thermoelectric power analyses. The XRD patterns of all prepared samples exhibited single phase with orthorhombic crystal structure (space group Pnma). Rietveld refinements were performed for all the patterns by using Fullprof software to extract the structural properties. The values of unit cell volume of samples tend to increase with the increment of dopant concentration, whereas the crystallite size values were decreased with dopant concentration. The microstructures of all the samples were studied using SEM, and elemental compositions were confirmed from the EDS results. Linear thermal expansion coefficients of all the samples were found to have moderate values in the temperature range from 30°C to 800°C. The electrical properties of all the system of samples were studied in the temperature range from 30°C to 400°C using DC fourprobe conductivity setup. It was found that all the samples exhibited semiconductor nature. Sr-content on the A-site suppress the electrical resistivity up to 10% of concentration and 5% dopant content exhibited the lowest electrical resistivity. The values of Seebeck coefficient found to vary from -160 µV/K to -124 µV/K with the increase of dopant content in the parent compound.

Abstract: The aim of this study is discussing the results achieved on undoped and Ni-doped bulk LaCoO₃ samples synthesized by solid-state reaction. The crystal structures of the samples were analyzed by x – ray diffraction (XRD) and Rietveld refinement of the XRD patterns was used to test the quality of the samples, the results of this procedure confirmed a single phase of LaCo_1-xNi_xO₃ for (x=0 and 0.05) with rhombohedral crystal structure (space group :). The main interest in this class of materials is the possibility of improving the values of Seebeck coefficient and electrical resistivity through chemical doping. The Seebeck coefficient and electrical resistivity were investigated from room temperature (RT) to 450 K, near RT the LaCoO₃ system showed a large negative Seebeck coefficient, but it changed to positive value with increasing temperature while the LaCo_0.95Ni_0.05O₃ composition showed a positive Seebeck coefficient throughout all the temperature range. Hence, within this study the Ni substitution led to decrease the electrical resistivity of the samples to one order of magnitude as a result of the partial substitution of Co³⁺ in LaCoO₃ by Ni²⁺. LaCoO₃ was chosen for this thermoelectric test because cobalt oxides have extensive applications.

Abstract: Tin Selenide, Lead Selenide, and Lead Telluride are known best thermoelectric materials for mid and high-temperature electric generation applications. The bilayer of these materials could enhance the quality of a thermoelectric generation. The present work deals with bilayer deposition of SnSe/PbTe and SnSe/PbSe in glass substrates using physical vapor deposition followed by annealing at 323K, 423K, and 523K. The structure and morphology of the films have been investigated by XRD, SEM, and FESEM studies. The thermoelectric pursuance of both bilayer thin films was studied with the temperature as a function in the range of 300K to 623K. Both films exhibit the maximum Seebeck coefficient. The electrical Conductivity and Power factor increased gradually for SnSe/PbTe thin films and SnSe/PbSe thin films for the samples annealed up to 573K and then decreases. The electronic thermal conductivity of both films was very low compared to the total thermal conductivity. The absolute thermal conductivity at room temperature was calculated by Transient Hot Wire (THW) method. The maximum Figure of Merit (ZT) value obtained for SnSe/PbTe and SnSe/PbSe at room temperature was 0.81 and 1.3 for 573K annealed thin films respectively.

Abstract: Thermoelectricity is the best technology for converting wasted heat into clean electrical energy. Calcium Bismuth cobaltites Ca_2.7Bi0_.3-xNd_xCo₄O_9+⸹ was synthesized using WOWs Sol-gel method with (x=0.0,0.05) doped with Neodymium. A structural study was carried out using the X-rays diffraction (XRD), which confirmed the Monoclinic structure of all the prepared samples. The Electrical properties were studied by using two-probe method. The thermal transport properties of the samples were measured at room temperature using the Advantageous transient plane source (ATPS) method. At room temperature thermal conductivity was measured. Seebeck coefficient as a function of temperature measurement revealed that doping Neodymium considerably increases the value of the Seebeck coefficient when compared to previously published values. At the end we measured the figure of merit (ZT).

Abstract: The thermoelectric properties of compounds with variable valence Mn_1-ХRe_ХS (0 ≤ X ≤ 0.2) in the temperature range of (80 – 1100) K are studied. The maxima on the temperature dependences of the Seebeck coefficient (thermal EMF) for all substitution concentrations and the change of the sign of the Seebeck coefficient from positive to negative with an increase in the substitution concentration in Mn_1-XYb_XS are determined. A model of impurity donor 4f-states is proposed and a satisfactory agreement with the data on the thermal EMF is obtained.

Abstract: Thermoelectric materials has made a great potential in sustainable energy industries, which enable the energy conversion from heat to electricity. The band structure and thermoelectric properties of Ni_(x)Zn_(1-x)Fe₂O₄ have been investigated. The bulk pellets were prepared from analytical grade ZnO, NiO and Fe₂O₃ powder using solid-state method. It was possible to obtain high thermoelectric properties of Ni_(x)Zn_(1-x)Fe₂O₄ by controlling the ratios of dopants and the sintering temperature. XRD analysis showed that the fabricated samples have a single phase formation of cubic spinel structure. The thermoelectric properties of Ni_(x)Zn_(1-x)Fe₂O₄ pellets improved with increasing Ni. The electrical conductivity of Ni_(x)Zn_(1-x)Fe₂O₄ pellets decreased with increasing Ni content. The electrical conductivity of Ni_(x)Zn_(1-x)Fe₂O₄ (x = 0.0) is (0.515 x10^-3 Scm^-1). The band structure shows that Zn_xCu_1-xFe₂O₄ is an indirect band gap material with the valence band maximum (VBM) at M and conduction band minimum (CBM) at A. The band gap of Ni_(x)Zn_(1-x)Fe₂O₄ increased with increasing Ni content. The increasing band gap correlated with the lower electrical conductivity. The thermal conductivity of Ni_(x)Zn_(1-x)Fe₂O₄ pellets decreased with increasing Ni content. The presence of Ni served to decrease thermal conductivity by 8 Wm^-1K^-1 over pure samples. The magnitude of the Seebeck coefficient for Ni_(x)Zn_(1-x)Fe₂O₄ pellets increased with increasing amounts of Ni. The figure of merit for Ni_(x)Zn_(1-x)Fe₂O₄ pellets and thin films was improved by increasing Ni due to its high Seebeck coefficient and low thermal conductivity.

Abstract: In this work, p-type thermoelectric material was produced by hot extrusion of pre-synthesized in injection molding machine Bi_0.5Sb_1.5Te₃ solid solution. During the research radial distribution of the Seebeck coefficient was confirmed and described in material’s cross section using thermal measuring probe. Such nonuniformity of the Seebeck coefficient is correlated with the strain-stress state of extrudate specifically with the distribution of accumulated strain intensity, which was obtained by mathematical modeling of extrusion process using the software package DEFORM.

Abstract: Successively forming GaSb islands by solid-phase epitaxy and covering them with a silicon layer, a nanostructured material containing 4 layers of GaSb nanocrystals (NCs) was grown on Si (111) surface. Due to a small size of the NCs (average height ~ 1.7 nm, average lateral size ~ 14 nm) and, as a consequence, to a significant quantum-size effect, a high electrical conductivity (~ 100 Ω^-1·cm^-1 at 600 K) together with a low thermal conductivity (~ 1 – 1.5 W·m^-1·K^-1 at 600 K) was obtained in the nanostructured material Si/NC_GaSb/Si. As a result, the thermoelectric figure of merit of the material has reached 0.82 at 600 K.

Abstract: The world is currently facing numerous challenges related to energy supply and consumption. Renewable energy sources are very important in view to enhance the worldwide energy needs and environmental effects. One of the important, cost effective and pollution free techniques for renewable energy source is the thermoelectric technology. Thermoelectric materials are of great importance as they convert the heat energy into electrical energy. Thermoelectric materials include tellurides, cobaltites and oxides. In present work, bismuth telluride doped with rare earth metal Gadolinium of different compositions i.e. 0.0 and 0.1 was synthesized by using the simplified sol-gel technique. For structural analysis including crystal structure, phase purity, crystallite size of samples and the lattice parameters, X-ray diffraction (XRD) was used. The structural analysis showed the rhombohedral structure of Bi₂Te_3. AC electrical properties i.e. ac conductivity, loss factor, dielectric constant and impedance studied as a function of frequency (20Hz-3MHz). AC conductivity increased with the increase in frequency while the loss factor, dielectric constant and impedance decreased with the increase in frequency. DC resistivity was analyzed using two probe method at room temperature. Thermal transport properties i.e. thermal conductivity (λ), thermal diffusivity (κ) and volumetric heat capacity(ρCp) are also measured along with the Seebeck coefficient at room temperature.

Abstract: Thermoelectric properties were simulated for low-dimensional atomistic model structures based on first-principles calculation. New methodology about the first-principles simulation on Seebeck coefficient at arbitrary temperature and carrier concentration is presented. Dependence of Seebeck coefficient on scale, temperature, and carrier concentration has been demonstrated for silicon and beta silicon carbide nanowire models. Compared with the corresponding bulk models, a significant increase of the absolute value of Seebeck coefficient can be observed owing to quantum confinement by dimensional reduction. By the simulation with considering the energy dependence of the relaxation time, the Seebeck coefficient from the viewpoint of first principles can be evaluated as a range determined by the scattering constants peculiar to particular scattering processes.