Thermoelectromotive Force Research Articles

Synthesis of nanometric iron oxide films by RPLD and LCVD for thermo–photo sensors

Iron oxide films were deposited on Si substrates by reactive pulsed laser deposition (RPLD) using a KrF laser (248 nm). These films were deposited too by laser (light) chemical vapor deposition (LCVD) using continuous ultraviolet photodiode radiation (360 nm). The deposited films demonstrated semiconducting properties. These films had large thermo-electromotive force (e.m.f.) coefficient (S) and high photosensitivity (F). For films deposited by RPLD the S coefficient varied in the range 0.8–1.65 mV/K at 205–322 K. This coefficient depended on the band gap (E g ) of the semiconductor films, which varied in the range 0.43–0.93 eV. The largest F value found was 44 Vc/W for white light at power density I≅0.006 W/cm2. Using LCVD, iron oxide films were deposited from iron carbonyl vapor. For these films, the S coefficient varied in the range −0.5 to 1.5 mV/K at 110–330 K. The S coefficient depended on E g of the semiconductor films, which varied in the range 0.44–0.51 eV. The largest F value of these films was about 40 Vc/W at the same I≅0.006 W/cm2. Our results showed that RPLD and LCVD can be used to synthesize iron oxide thin films with variable stoichiometry and, consequently, with different values of E g . These films have large S coefficient and high photosensitivity F and therefore can be used as multi-parameter sensors: thermo–photo sensors.

Quench Detection Method of HTS Model Coil Using a Series-Type Thermocouple

This paper proposes a quench detection method applied to a HTS coil and also discusses the results of tests on an HTS BSCCO wire and an HTS YBCO coil. A series-type thermocouple was fabricated to detect quench, where several thermocouples were welded in series. As the series-type thermocouple has many points of detection, variation in temperature was detected at each point by using thermo-electromotive force. The feasibility of the proposed method was investigated through the quench detection tests on the YBCO coil. This method has advantages such as a simple structure and cost effectiveness and also protects the HTS coil by detecting partial quench and its propagation.

Power Properties of the Transverse Short-Circuited Thermoelement

The short-circuited thermoelement (SCTE) with slanted shorting was studied in electric power generation mode by means of computer simulation. The basic power characteristics and the distribution of physical fields in the thermoelement were obtained. The transverse thermo-electromotive force (EMF) and efficiency of the SCTE were studied as functions of the material, number, cross-sectional area, and orientation with respect to the temperature gradient of the shorting elements. The optimal parameters of the thermoelement to achieve maximum efficiency were determined. Recommendations for SCTE optimization are described.

Structural, electrical, and optical characterizations of laser deposited nanometric iron oxide films

The structural, electrical, and optical characteristics of nanometric Fe2O3−x films fabricated on ⟨100⟩ Si and SiO2 substrates by ablating an iron target with a KrF excimer laser in low pressure (0.05–1.0 Pa) O2 atmosphere are reported. The thickness of films fabricated with 4000 laser pulses is ∼80 nm for samples deposited at the lowest pressure (0.05 Pa) and decreases gradually to 50 nm at the highest used pressure (1.0 Pa). The film mean composition results close to FeO at lower pressures (0.05–0.10 Pa) and to Fe2O3 at higher pressures (0.5–1.0 Pa). From glazing incidence x-ray diffraction spectra, it was inferred that deposits are poorly crystallized, especially the ones prepared at relatively high oxygen pressures (0.5–1.0 Pa). Scanning electron microscopy inspections show that surfaces are plane and uniform, with very rare (<0.1 μm−2) submicron droplets. From x-ray reflectivity spectra, surface roughness results very low (0.1–0.5 nm, increasing with O2 pressure). The films present a semiconductor behavior, with electrical energy gaps increasing from 0.43 to 0.93 eV with increasing O2 pressure, while the optical energy gap varies from 1.60 eV (0.05 Pa) to 1.74 eV (1.0 Pa). Very high thermoelectromotive force coefficient values were measured (up to 1.65 mV/K). It is also shown that films present promising gas sensing properties.

Thermoelectric Performance of p-Type Mg<SUB>2</SUB>Si<SUB>0.25</SUB>Sn<SUB>0.75</SUB> with Li and Ag Double Doping

The single-phase of p-type Mg2Si0.25Sn0.75 with Li and Ag double doping were prepared by the liquid-solid reaction and hot-pressing methods. All samples thus obtained were identified by XRD as single-phase solid solutions with an anti-fluorite structure. The effects of Li and Ag double doping on thermoelectric performance were investigated at temperature differences (ΔT) of 0 to 500 K. The thermoelectromotive force (E) of the Li-25000 ppm single-doped sample was determined to be 88 mV at ΔT=500 K. For the Li-20000 ppm and Ag-5000 ppm double-doped sample, the E value became larger (92 mV) after Ag substitution. A maximum E value of 97 mV was obtained for the Ag-25000 ppm single-doped sample and the Li-5000 ppm and Ag-20000 ppm double-doped sample. Mean resistivity (rm) at ΔT=500 K decreased by double doping and showed a minimum value of 2.94×10−5 Ωm for the Li-5000 ppm and Ag-20000 ppm double-doped sample. The maximum effective power (P=E2⁄4rm) increased with ΔT. The P values of single-doped samples at ΔT=500 K were 38 Wm−1 for Li single-doped and 72 Wm−1 for Ag single-doped samples. P for the Li-20000 ppm and Ag-5000 ppm double-doped sample was 64 Wm−1, which was an improvement of about 90% compared with the Li single-doped sample. The maximum value of P at ΔT=500 K was 80 Wm−1 for the Li-5000 ppm and Ag-20000 ppm double-doped sample, which was an improvement of about 10% compared with the Ag single-doped sample.

C13 切削工具一体型WC-Cr極小温度センサアレイの開発(OS5 加工計測・評価(1))

In this paper, a new temperature sensor was proposed in order to measure cutting temperature fields continuously with a quick response regardless of the conductivity of a work. It has thermocouple array constructed by a tool and sputtered metallic lines, which are embedded into a cutting tool rake face. Here is a process flow. The trenches and electrodes were milled by femto second laser. And, insulating films and metallic lines were sputtered on the rake face. Finally, unwanted films were removed selectively by polishing. The thermo electromotive force of our sensor was converted to temperature based on a calibration curve obtained by experimentally. Cutting experiment showed that cutting temperature at the rake face could be measured by our sensor.

C11 切削温度測定のための熱起電力特性の機上測定(OS5 加工計測・評価(1))

C11 切削温度測定のための熱起電力特性の機上測定(OS5 加工計測・評価(1))

Nonlinear carrier transport within gigahertz-terahertz frequencies in spatially non-uniform InSb

Influence of a dc electric field, microwave and terahertz (up to 1.63 THz) excitation on the carrier transport in moderately compensated n-InSb<Cr> containing graded n/n+ junction is investigated. Hot electron thermo-electromotive force and field dependences of the dc-conductivity were measured within 10-110 K. Peculiarities of electron gas heating and low-temperature electron transport can be attributed to the potential fluctuation effects due to random spatial distribution of impurity density in high-resistivity InSb<Cr> crystal.

Mott criterion application to analysis of electrical conductivity in Na-β-aluminates doped by yttrium

The mechanism of electrical conductivity in yttrium-doped Na-β-aluminate has been investigated in terms of the Mott criterion in the range from room temperature to 1073 K. The activation energies for electrical conduction and thermoelectromotive force are determined from high-temperature measurements. The results obtained and the data derived from optical measurements are in satisfactory agreement. It is shown that electrical conductivity is determined by nonlocalized states in the temperature range from 973 to 1073 K and by localized states in the range from room temperature to 973 K.

Miniature diamond anvil cell for broad range of high pressure measurements

A miniature versatile nonmagnetic diamond anvil cell for diverse physical property measurement under cryogenic environments and high magnetic fields at high pressure has been developed. Several such cells have been manufactured and tested in the Physical Properties Measurement System (PPMS) by Quantum Design at high pressures and low temperatures. The cells have good pressure stability during temperature scans down to helium temperatures and back to room temperature. The cells have been tested in strong magnetic fields and demonstrated excellent nonmagnetic properties. The wide-angle side openings give the possibility to use this cell as a "panoramic cell" in synchrotron experiments requiring large angle off-axis access. The possible experiments, which may use this cell, include spectroscopic experiments (optical, synchrotron Mossbauer, Raman, x-ray emission, etc.), different types of x-ray diffraction experiments, transport measurements (resistivity, magnetoresistivity, thermoelectromotive force, etc.), measurements of susceptibility, and many other conventional and synchrotron experiments at very low temperatures and in strong magnetic fields.

Thermoelectromotive Force of Some Redox Couples in an Amide-type Room-temperature Ionic Liquid

Reaction entropies of some metal complex redox couples in an amide-type room-temperature ionic liquid, 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide (BMPTFSA) have been estimated by measuring the thermoelectromotive force at a non-isothermal cell. It is suggested that the reaction entropy is dependent on the difference in the charge densities of the oxidant and reductant of a redox couple, probably related to the coulombic interaction between the redox species and the ions composing the ionic liquid.

Fabrication of Thermoelectric Module by A New Manufacturing Process and Its Performance

A new process for manufacturing thermoelectric modules was proposed, and thermoelectric performance of the modules were evaluated. Both powders of p-type FeCo3Sb12 and n-type Co0.92Ni0.08Sb2.96Te0.04 compounds were alternately filled into 4×4 square holes of an insulating mold. The powders in the holes were compacted and sintered simultaneously at 903 K in vacuum for 20 min under the pressure of 60 MPa by a pseudo hot isostatic pressing (pseudo HIP) method, in which one-directional load is transmitted isostatically to the sample through the alumina powder filled around the sample. The sixteen sintered elements (1.9 mm×1.9 mm×9.0 mm) in the mold were electrically connected in series using silver paste. Then, a thermoelectric module was constructed by parallel sandwiching the mold with glass plates of 0.5 mm in thickness. The thermoelectromotive force was 591 mV at the temperature gradient of 356 K, and the internal resistance in the module was 2.77 Ω. In this case, the output power of 31.5 mW was obtained and the power density of 576 W/m2 was estimated. The value of output power was less than that of the theoretical calculation.

Influence of oxygen argon ratio on the structural, electrical, optical and thermoelectrical properties of Al-doped ZnO thin films

In this study, high quality of Al-doped ZnO (AZO) thin films were deposited at different oxygen argon ratio by direct current (DC) reactive magnetron sputtering using a Zn target (99.99%) containing Al of 1.5%. The obtained films were characterized and analyzed by X-ray diffraction (XRD) and ultraviolet–visible and infrared light spectrophotometer. The electrical properties had been investigated by van der Pauw method. It was also found that oxygen argon (O 2/Ar) ratio had great influence on the properties. The results show that AZO thin films are polycrystalline with a preferred (0 0 2) orientation. The film stress increases with increasing O 2/Ar ratio. The lowest resistivity of 1.306×10 −3 Ω cm was obtained for the AZO thin films prepared at O 2/Ar ratio of 0.3/27. Hall mobility decreases with increasing the O 2/Ar ratio. With increasing O 2/Ar ratio, the transmittance of the AZO thin films has no evident changes. There is a strong absorption in the ultraviolet region. The optical absorption edge is found to shift to the longer wavelength with the increase of O 2/Ar ratio. The measurements show that there is a striking Seebeck effect in the AZO thin films, and their thermoelectromotive force is linearly increased with increasing temperature difference (Δ T). With increasing O 2/Ar ratio and resistance of samples, thermoelectric power (TEP) decreases.

Transport properties and ferromagnetism of Co x Mn1 − x S sulfides

We have studied the resistivity and thermoelectromotive force (thermo emf) in a temperature range of T = 80–1000 K, the magnetic susceptibility and magnetization in a temperature range of T = 4.2–300 K at an external magnetic field of up to 70 kOe, and the structural characteristics of CoxMn1−xS sulfides (0 ≤ x ≤ 0.4). Anomalies in the transport properties of these compounds have been found in the temperature intervals ΔT1 = 200–270 K and ΔT2 = 530–670 K and at T3 ∼ TN. The temperature dependences of the magnetic susceptibility, magnetization, and resistivity, as well as the current-voltage characteristics, exhibit hysteresis. In the domain of magnetic ordering at temperatures below the Neel temperature (TN), the antiferromagnetic CoxMn1−xS sulfides possess a spontaneous magnetic moment that is explained using a model of the orbital ordering of electrons in the t2g bands. The influence of the cobalt-ion-induced charge ordering on the transport and magnetic properties of sulfides has been studied. The calculated values of the temperatures corresponding to the maxima of charge susceptibility, which are related to a competition between the on-site Coulomb interaction of holes in various subbands and their weak hybridization, agree well with the experimental data.

Advanced Thermal Energy Conversion of Temperature under 300.DEG.C. by Thermoelectric Conversion Method

Many approaches have been developing for energy conversion throughout the world. However, it is difficult to achieve the global warming countermeasure based on “The Kyoto protocol”. Until now effective utilization of low temperature thermal energy (under 300°C) is not advancing one. For example, effective utilization method has not been established for waste heat energy which arise from industry machine tools, automobiles, internal combustion engines and thermal energy from natural environment, etc.In this paper, we reported the experiment for effective utilizing of low temperature (under 300°C) thermal energy conversion. The device used for the measurement is a copper thermo device. Thermo electromotive force of 150mW/cm2 was obtained at 200°C. The obtained thermo electromotive force is about 15 times higher in comparison with generally used alumal-chromal thermocouple. Our aim is that utilizes low temperature thermal energy effectively by converting into electricity.

Correlation between electron state density change and the electrical resistivity and magnetic permeability changes in the nanostructured powder of the NiMo alloy

The nanostructured powders of the Ni 95.4Mo 4.6 and Ni 99Mo 1 alloys (average crystallite dimensions of 14 and 21 nm) were obtained by the electrochemical deposition from ammonium solutions of nickel and molybdenum salts. The method of differential scanning calorimetry (DSC) and measurement of temperature dependence of the powder's electrical resistivity, magnetic permeability and the thermoelectromotive force were employed to examine structural changes of the powders. The nanocrystalline alloys Ni 95.4Mo 4.6 and Ni 99Mo 1 were stable up to about 460 K. The thermal stabilization of the alloys takes place within the temperature interval of 460–570 K. As a result of this process, a decrease in the electrical resistivity and increases in magnetic permeability as well as electron state density in the proximity of the Fermi level are observed. The crystallization temperature depends upon the current density of powder formation. The nanocrystalline alloy Ni 95.4Mo 4.6 obtained at j=70 mA cm −2 becomes crystallized in the temperature range between 650 and 840 K, while the Ni 99Mo 1 alloy obtained at j=180 mA cm −2 crystallizes in the 580–950 K temperature interval. The electrical resistivity and magnetic permeability of the nanocrystalline alloy decreased while the alloy's electron state density near the Fermi level increased after the process of crystallization took place. The electrical resistivity decrease recorded during the structural changes was due to an increase in the electron state density in the proximity of the Fermi level, as well as to an increase in the mean free path of the conducting electrons.

Deposition of thin films for sensors by pulsed laser ablation of iron and chromium silicide targets

Thin films were deposited by KrF laser ablation of CrSi 2 and β-FeSi 2 targets with the aim to obtain silicide thin films and layers with narrow band gap for sensor applications. The CrSi 2-based films exhibit both semiconductor and metal properties, depending on the deposition conditions. Thus, the film of d ≅ 40 nm thick, deposited on Si at 740 K, presents a band gap E g ≅ 0.18 eV, and large thermo electromotive force (e.m.f.) coefficient α ≅ 1.0–1.4 mV/K at 300 ≤ T ≤ 340 K and a coefficient of tensosensitivity ( R– R 0)/ R 0 ɛ ≅ 5. The film with the same thickness, but deposited on SiO 2 at 740 K, presents a metal behavior at 125 ≤ T ≤ 296 K and a semiconductor one at 77 ≤ T ≤ 125 K. Its coefficient α varies in the range 5.0–7.5 μV/K at 300 ≤ T ≤ 340 K. The 750 nm thick film deposited on SiO 2 at 740 K exhibits only semiconductor behavior in the range 296–77 K with E g ≅ 0.013 eV and α ≅ 10–15 μV/K at 293 ≤ T ≤ 340 K. The coefficient of tensosensitivity for these films is changing in the range 2–5. The β-FeSi 2-based films deposited on SiO 2 at 295 ≤ T ≤ 740 K show only semiconductor behavior. The thicker the film, the higher E g: d ≅ 150 nm, E g ≅ 0.032 eV; d ≅ 70 nm, E g ≅ 0.027 eV; d ≅ 60 nm, E g ≅ 0.023 eV. The higher E g , the higher coefficient α. The coefficient of tensosensitivity for these films varies in the range 2.3–4.7. The more the semiconductor phase content in the deposited film, the higher are the values of α and ( R– R 0)/ R 0 ɛ.

On the melting temperature of B6O

Superhard B6O [1] is the most extensively studied boron suboxide [2]. However, there are no data in the literature on its melting temperature. According to [3], at atmospheric pressure B6O decomposes into boron and oxygen even at temperatures of the order of 2000 K, therefore, the congruent melting of this phase can evidently be observed at high pressures only. In the present study, the diffraction with synchrotron radiation was used to define the B6O melting temperature in the pressure range from 4 to 6 GPa. B6O was synthesized by the interaction of high purity amorphous boron (99.99%, Alfa) and B2O3 (99.999%, Aldrich Chem. Co.) taken in the stoichiometric ratio at 5 GPa and 2100 K following the procedure [4]. According to the X ray analysis, the resultant product was crystalline B6O (R⎯3m, a = 5.366 A, c = 12.331 A) that contained no impurities of foreign phases. Experiments on melting B6O at high pressures and temperatures were carried out in a MAX80 multianvil apparatus [5]. The diffraction patterns were taken in situ by the energy dispersive X ray diffractometry (θ = 4.558±0.002°) at the F2.1 beamline of the Doris III storage ring (HASYLAB DESY). The temperature calibration in the range from 800 to 2200 K was performed using Pt90/Rh10–Pt and W75/Re25–W97/Re3 thermocouples without correction for the pressure effect on the thermoelectromotive force. The cali bration curve obtained was linearly extrapolated to the high temperature region up to 2800 K. The pressure in the cell at dif ferent temperatures was defined using the p, V, T equation of state of highly ordered graphite like hexagonal boron nitride [6]. To isolate the sample from a graphite heater, a capsule of pyrolytic graphite was employed. At 5.8 GPa the disappearance of B6O lines was observed in the range from 2670 to 2750 K (figure), which was accompanied by the appearance of a characteristic diffuse halo. This has allowed us to assess the melting temperature of boron suboxide at 2710±40 K, which is higher than the melting temperature at this pressure of β rhombohedral boron by 250 K [7]. The cool ing of the melt to about 2100 K at a rate of ~ 10 K/s was accom panied by the crystallization of B6O as evidenced by the appear ance of the 104 and 021 lines of this phase in the diffraction spectra (see figure). At 4.3 GPa the melting of B6O was observed at temperatures of about 2620 K, which points to a positive slope (~ 60 K/GPa) of the melting curve in the pressure range from 4 to 6 GPa. The authors thank O.O. Kurakevych and V.Z. Turkevich for their participation in discussions of the results and acknowledge the financial support of the Agence Nationale de la Recherche (grant NT05 3_42601) and NATO (CLG # 981851). 15 20 25 30 35 40 45 00 6 02 1 10 4 10 1 01 2 00 3 10 1 2090 K

Measurement System of Instantaneous Surface Temperature on Combustion Chamber Walls in an Internal Combustion Engine by Thin-Film Thermocouples

The state of heat loss from combustion gas to combustion chamber walls during the cycle in an internal combustion engine can be evaluated from instantaneous surface temperature of the walls measured by thin-film thermocouples (TFTs). Not only a suitable temperature probe but also an appropriate measurement system is necessary for accurate measurement.TFTs developed by the authors' group were designed and fabricated so that disturbance of the temperature filed could be minimized when they were embedded into combustion chamber walls. Appropriate measurement circuits and devices are necessary for accurate measurement of thermoelectromotive force generated by the TFTs because it changes very quickly as the crank angle, and the amplitude of its fluctuation is considerably small, usualy less than 3 mV. Therefore, the authors' group established a measurement system which consists of measurement circuits of thermoelectromotive force, an A/D (analog to digital conversion) system and a data processing device. The authors' measurement circuit has an advantage of being noise-free and quick in switching channels. On the other hand, the A/D system is of high accuracy and synchronizes with the engine operation. Furthermore, meaningfully reproductive data is generated by the data processing device. In this report, the authors' measurement system is presented.

A Fast-Response Thermopile Photodetector Fabricated by a Photolithography Technique Combined with Laser-Beam Machining

A micrometer-scale thermopile formed on Si substrate using a photolithography technique combined with laser-beam machining is described. Initially, the surface of an 11-mm-square and 0.3-mm-thick Si substrate was oxidized to grow a SiO2 thin-film. A 300-μm-long, 100-μm-wide and 0.5-μm-thick SiO2 air bridge was then formed on the Si substrate using a photolithography technique. Next, copper and constantan were evaporated in layers on the middle of the air bridge. This evaporated thin film functioned as a type-T thermocouple. Then, in order to improve the sensitivity of the thermocouple, three of the type-T thin-film thermocouples were shaped by cutting the evaporated film into three regions using a laser-beam machining technique. Finally, the thermopile was completed by connecting the three thermocouples in series, locating their hot junctions on the center of the air bridge and cold junctions on the pad areas used as electrodes. Because the heat capacity and the heat dissipation of the hot junction areas differ from those of the cold junction area, a temperature difference occurs between the hot and cold junctions when the thermopile receives radiation. This temperature difference generates a thermo-electromotive force between the cold and hot junctions, which is a measure of the intensity of the incident radiation. Due to a small heat capacity combined with a relatively large radiation reception area, the time-constant of this type of thermopile for light-illumination was found to be less than 1 ms, which was more than ten times faster than that of conventional thermopiles presently on the market.