Papers by Keyword: Seebeck Coefficient

Abstract: LaSr₃Fe_3-xMn_xO_10-δ (x=0.0-0.8) mixed conductors with layered perovskite structure were prepared via citric acid method. XRD analysis showed that the cell volume decreased with Mn content. The fraction of Fe⁴⁺ concentration to the concentration of tetravalent ions decreased with the increase of Mn content. The decrease of average valence state (V_B) of transition metals of LaSr₃Fe_3-xMn_xO_10-δ samples with the increase of temperature gave rise to the drop of p type charge carriers and the increase of oxygen vacancies. According to the relationship between V_B and the numbers of the configurations of transition metals in LaSr₃Fe_3-xMn_xO_10-δ , the possible filling states of 3d orbitals of Fe and Mn ions at 700 °C and 800 °C were given. The variations of conductivities of LaSr₃Fe_3-xMn_xO_10-δ samples were interpreted on the basis of the variation of V_B and δ with temperature and Mn content, respectively. Scanning Kelvin probe measurement results revealed that the surface potential of x=0.6 sample was the highest while x=0.8 sample was the lowest. The higher the surface potential, the higher the energy needed for an electron to be released from the sample.

Abstract: CaMnO₃ (CMO) thermoelectric material is large Seebeck coefficient but high electrical resistivity. To reduce electrical resistivity by adding carbon nanotubes (CNTs) in CMO material and may be decreased Seebeck coefficient. In this work, we simulated electronic structure of CMO and CNTs-added CMO by DV-Xα method to investigation of power factor and enhance the thermoelectric performance. The Seebeck coefficient and electrical resistivity were calculated by Maxwell-Boltzmann distribution and Mott’s law to investigate power factor. The DV-Xa calculated show the energy level and density of state (DOS) of CMO and CNTs-added CMO demonstrated that the energy gap reduces from 3.33 eV to 0.19 eV affect to enhance the power factor of CMO with Seebeck coefficient and electrical resistivity are decreases. The power factor of CNTs-added CMO was increased with increasing CNTs content.

Abstract: In order to get an accurate online measurement for the transient cutting temperature in precision, in an ultra-precision cutting process,a temperature measuring device should be assessed whether it can obtain precise magnitude readings and variables of which are measured accurately. The just produced thin-film thermocouple used to measure tool cutting temperature must be correctly calibrated[3,4] , however traditional calibrating process problems rely on manual operation completely with lots of problems such as low efficiency, high labor intensity and large error. this paper proposes an automatic calibration system for thin-film thermocouple by using temperature measuring furnace, data acquisition card and computer-based software. The system makes an automatically and intelligently calibration process. By using a high-precision data acquisition card and precision amplifier circuit, eight thermocouples can be calibrated at the same time automatically which effectively shortens the calibration time and improves the accuracy. Use temperature metering furnace to control data acquisition. Secondary error from using standard thermocouple and other methods to collect the temperature metering furnace real-time temperature is eliminated. The system software modules consist of data reading, data processing, data display, database operation, data query and report generation module. The experimental results show that nonlinear fitting error is less than 0.6% within the temperature measurement range, which meets the requirement of the secondary precision of thermocouple error. This paper intends to provide a new calibration method for thermocouple temperature measurement tool development and production[7].

Abstract: Single phase samples of Na_1-xCa_xCo₂O₄ (with x = 0, 0.1, 0.2 and 0.3) are prepared by utilizing a solid state reaction process, and the Ca²⁺ substitution effect on thermoelectric properties is then observed. On the samples, the increment of Ca²⁺ substitution results in the increase of resistivity and thermo power properties. The Ca²⁺ substitution in NaCo₂O₄ reduces charge carriers of the samples. This phenomenon indicates that there are many holes in the samples and it is consistent with the positive sign of thermo power. It demonstrates that the Ca²⁺ substitution is effective to enhance thermoelectric properties.

Abstract: We investigate thermoelectric characteristics of SiGe nanostructures for realizing high-sensitive infrared photodetector applications. In this paper, for future Ge and SiGe nanowires, we fabricate p-type Ge-on-insulator (GOI) substrates by a direct wafer bonding process. We discuss the annealing effect on the GOI substrate in the process and measure its Seebeck coefficient in the temperature range of 290-350 K. The Seebeck coefficient of the GOI layers is almost identical with the reported values for Ge. This result confirms that the measured Seebeck coefficient of GOI layers is not influenced by the buried oxide (BOX) layer and the Si substrate.

Abstract: The Seebeck coefficient of P-doped ultrathin Si-on-insulator (SOI) layers is investigated for the application to a highly-sensitive thermopile infrared photodetector. It is found that the Seebeck coefficient originating from the phonon drag is significant in the lightly doped region and depends on the carrier concentration with increasing carrier concentration above ~5×10¹⁸ cm^-3. On the basis of Seebeck coefficient calculations considering both electron and phonon distribution, the phonon-drag part of SOI Seebeck coefficient is mainly governed by the phonon transport, in which the phonon-phonon scattering process is dominant rather than the crystal boundary scattering even in the SOI layer with a thickness of 10 nm. This fact suggests that the phonon-drag Seebeck coefficient is influenced by the phonon modes different from the thermal conductivity.

Abstract: In this paper we reported the electrical conductivity and thermoelectric characterization of silver (Ag) and antimony (Sb) co-doped lead telluride bulk materials, which have been synthesized using solid state microwave technique. The doping level has performed first-principle calculations for the AgPb_mSbTe_m+2 (LAST-m) (m = 0, 2, 4, 6, 8 and 10) to clarify the effect of simultaneous doping of Ag and Sb on PbTe. The Hall effect and thermoelectric measurements have shown n-type conductivity in AgPb_mSbTe_m+2 samples. The samples show large and negative values of the Seebeck coefficient and moderate electrical conductivity. The Seebeck coefficient increased with doping levels increases at m=0 to 10. The value of the Seebeck coefficient is −419.69 μVK⁻¹ for AgPb₈SbTe₁₀ at 338 K. It has been found that AgPb₈SbTe₁₀ sample has a higher thermoelectric power factor 1.87 mW K^-2 m^-1 at 310 K.

Abstract: Performance of current temperature sensor is not satisfactory on monitoring transient temperature of cutting edge. A temperature-testing cutter is presented in this paper and analysis of Seebeck coefficient on thin film thermocouple is proposed with experiments. Thin film thermocouple is embedded into the cutting edge using magnetron sputtering technology. According to the fact that electrical conductivity can be replaced by the multiplication of electron mean free path λ and effective Fermi surface area A, a universal formula of thermoelectric power is given based on the diffuse thermoelectric power equation put forward by Mott and Jones. Using the expression of electron mean free path in gas model λ, the relationship of thermoelectric power between thin film and bulk material can be deduced. Result shows that the main influential factor of Seebeck coefficient is film thermal junction thickness. In addition, the Seebeck coefficient of different junction size and film thickness were tested by LabVIEW automatic calibration system. The experimental data indicates that Seebeck coefficient is determined by thermal junction thickness, and the sensor is found to be linear from room temperature up to 600°C while the Seebeck coefficient of thin film thermocouple becomes closer to standard thermocouple as the film thickness increments. However, junction size does not have a major influence on the Seebeck coefficient which is agreed by both theoretical analysis and test.

Abstract: Thermoelectric cells and Solar cells are source of harvesting energy from heat and light respectively. In this study both are fabricated on a single cell using n-Si and p-Si single crystal strips.Later, temperature gradient cells are also fabricated . The fabricated Phtoto-thermoelectric cells and Temperature gradient celss are investigated, showing improvement in seebeck effect.

Abstract: The polycrystalline Na-doped CuAlO₂ ceramics were obtained by solid state reaction method. The mixture of high purity grade of CuO, Al₂O₃ and NaNO₃6H₂O powders was ground and then pressed by using uniaxial pressure. The obtained pellet was sintered in air at 1,423 K for 24 h. XRD patterns showed the crystal structure of the as-sintered Cu_1-xNa_xAlO₂ (0x0.05) belonging to rhombohedral, space groupalong with the CuO and CuAl₂O₄ phases. The minimum resistivity value around 4.48x10² Ωcm and maximum hole concentration around 2.04x10¹⁶ cm^-3 were observed for x=0.03 at room temperature. The properties of Seebeck coefficient and electrical resistivity were measured in the high temperature ranging 300 to 700 K. The results of electrical resistivity, Seebeck coefficient and power factor values decrease with increasing Na content. The calculated activation energy of conductivity (in the range of 160-250 meV) is larger than that of thermopower (in the range of 26-83 meV) which suggests that the conduction mechanism may be determined as a small polaron hopping type.