Thermal Electromotive Force Research Articles

Effect of Co doping on structural, optical, electrical and thermal properties of nanostructured ZnO thin films

Nanocrystalline Zn1−xCoxO (where x varies from 0 to 0.04 in steps of 0.01) thin films were deposited onto glass substrate by the spray pyrolysis technique at a substrate temperature of 350 °C. The X-ray diffraction patterns confirm the formation of hexagonal wurtzite structure. The crystal grain size of these films was found to be in the range of 11−36 nm. The scanning electron micrographs show a highly crystalline nanostructure with different morphologies including rope-like morphology for undoped ZnO and nanowalls and semispherical morphology for Co-doped ZnO. The transmittance increases with increasing Co doping. The optical absorption edge is observed in the transmittance spectra from 530 to 692 nm, which is due to the Co2+ absorption bands corresponding to intraionic d-d* shifts. The direct and indirect optical band gap energies decrease from 3.05 to 2.75 eV and 3.18 to 3.00 eV, respectively for 4 mol% Co doping. The electrical conductivity increases with increasing both the Co doping and temperature, indicating the semiconducting nature of these films. The temperature dependence thermal electromotive force measurement indicates that both undoped and Co-doped ZnO thin films show p-type semiconducting behavior near room temperature. This behavior dies out beyond 313 K and they become n-type semiconductors.

Mechanisms of the thermal electromotive force, heating and cooling in semiconductor structures

A comprehensive study of the mechanisms of the thermal electromotive force, heating and cooling originated by a temperature gradient and an electric current in semiconductor devices is reported. The Seebeck, Peltier, Joule and Thomson phenomena are studied self-consistently under the approximation of weak electric current and temperature gradient. Analytical calculations show that the contributions of each effect to the temperature distribution are commensurable. A new formulation and interpretation of the Thomson effect are given. Additionally, attention is paid to some questions of nonequilibrium thermodynamics of thermoelectric and electrothermic phenomena, that demand some clarification.

ICONE23-2068 MODELING OF FUEL KERNEL SURFACE PROFILE BASED ON RESULTS OF FUNCTIONAL ELECTROPHYSICAL DIAGNOSTICS

Plastic deformation of materials is localized in surface layers of the deformed item as separate spots of different intensity. Initial stages of deformation are characterized by single slip lines that transit to a dense set of parallel lines (slip packs). As deformation grows, shear bands typical of the volume microstructure are formed on the surface along with surface deformation waves. On the whole this is manifested as the material surface deformation activities. These lead to changes in the surface properties: mechanical, optical and electric. The latter can be studied by using structure-sensitive contact techniques, i.e. electric resistance measurements, thermal electromotive force and contact potential difference (Surin V., Evstjuhin N., Grisha S., 1996). The first two techniques are used to study structural failures in the volume and the contact potential difference depends primarily on conditions of the material surface. The surface deformation activity is linked with the yielding process in near-surface layers; even if the applied stress is significantly lower the yield stress. This is because process-induced stress points are on the surface (Shtremel M., 1997). Different models and assumptions are used to study into the surface deformation activity.

Specific features of the thermal electromotive force in Bi quantum wires in transverse magnetic and electric fields

The thermal electromotive force (emf) in Bi quantum wires has been calculated in the model of potential in the form of a paraboloid of revolution in a uniform magnetic field H, which is normal to the axis of the studied nanostructure, and in a direct-current (dc) electric field E ‖ H. It has been shown that, with an increase in E, the thermal emf αxx is described by a nonmonotonic function at different values of H. A physical interpretation of this behavior of αxx as a function of E is proposed with account for the interaction between carriers and the rough surface of the nanowire.

Phase Transformation in Multicomponent Ni<sub>3 </sub>(Mn,Ti) Alloys

The paper presents neutron diffraction analysis and X-ray investigation of ordered alloys Ni3(Mn,Ti) within the concentration range from 0 to 12.5 at.% Ti. The significant effect of the third alloying element Ti on the atomic long-range order was observed in superstructure L12 of alloy Ni3Mn. Experimental study has showed that a rapid quenching in ice water does not provide disordered Ni3(Mn,Ti) alloys. The two-phase region of internmetallic bonds was detected in compounds L12 and D024. The paper presents results estimation of electrical resistivity, normal and abnormal values of hall coefficient, Nernst–Ettingshausen effect, thermal electromotive force, and average atomic magnetic moment in quenched and annealed Ni3(Mn,Ti) alloys. Positive values of abnormal hall coefficient and Nernst–Ettingshausen effect were detected that confirms the predominant contribution of antiparallel spin 3d holes in conductivity. It is shown that in 2.2 at.% annealed Ti alloys ordering promotes 3d electron localization.

Effect of Mould Heating Temperature on Cooling Rate of the Melt upon Bronze Crystallization

The article presents the cooling curves of the tin-leaded bronze melt (consists of 10% of lead, 10% of tin, and 80% of copper) being poured in the moulds of various thermal conductivities: massive cast iron chill mould (with the 1:8 cast mass to mould mass ratio) and graphite mould. The curves were plotted for the moulds previously heated to the temperatures of 20; 200; 400; 600; 800 °С. Plotting of the curves was performed with the use of the device Thermograph designed at Tomsk Polytechnic University. The device records thermal electromotive force values of the chromel-alumel thermocouple and converts them into temperature values. The cooling curves are used to determine melt cooling rates within the temperature range involving the crystallization range. It is shown that under similar conditions the cooling rate when casting in cast iron mould is 30-40% higher than in the case of casting in graphite mould. The data given in the paper indicate that preheating of the mould enables us to considerably reduce the cast cooling rate and prolong the period of the melt being in liquid state. It is worth mentioning that cooling rate values of the preheated and non-heated casting moulds are most vividly observed at the initial moments after the melt pouring. When decreasing the casts’ cooling to 300-400 °С the cooling rates tend to be identical. In the article, the numerical data of cooling rates for various mould heating temperatures are presented.

Generation and Superposition of Concentration and Heat Waves Under Exothermic Reactions in Powder Systems

The superposition of reaction waves, leading to energy concentration in local regions, is revealed in studying the thermal kinetics of interaction in mixtures with exothermic reactions during contact melting. The local energy relaxes through spontaneous emission of charged particles. This influences the thermal electromotive force and allows the dynamics of reaction wave interaction to be followed in the process. In these cases, synthesis and reaction sintering are uncontrolled.

Electrical and elastic properties of an array of carbon nanotubes after irradiation by high-energy electrons

The effect of the irradiation of arrays of annealed and unannealed multiwalled carbon nanotubes (CNTs) by electrons with an energy of 21 MeV and a dose of 2.2 × 1017 el/cm2 on their electrical conductivity, thermal electromotive force, and elasticity coefficient is studied. It is established that the irradiation of annealed nanotubes considerably decreases (by nearly a factor of two) their electrical conductivity and coefficient of elasticity in the material pressing direction and increases their thermal electromotive force by nearly 1.5 times. The effect of the same dose of electron irradiation on an array of unannealed CNTs also leads to an appreciable decrease in its coefficient of elasticity, but favors a considerable increase in the electrical conductivity and thermal electromotive force of the material. The observed effects are discussed in relation to the specifics of the formation of radiation defects in CNTs and their interaction with primary defects in unannealed specimens.

高精度铂电阻测温系统

Interfered by factors such as short and long term drifts of a constant current source and the thermal electromotive force of a wire,the measurement accuracy of conventional 4-wire Pt-resistance temperature measurement system is hard to achieve the order of 0.1℃.After analyzing the principle error of an enhanced 4-wire Pt-resistance temperature measurement method,a high precision Pt-resistance temperature measurement system was designed.By using a reference resistance with small temperature coefficient and high stability as the Pt-resistance measurement datum,the temperature measurement error caused by the long term drift of a constant current source was eliminated.At the same time,the short-term drift of the constant current source was suppressed by temperature control using a Thermoelectric Cooler(TEC).For wire thermal electromotive force,it was a great advantage to be short-term invariable.Measured under the positive and negative current conditions,the two voltages on Pt-resistance were subtracted.In this way,the effect of wire thermal electromotive force was eliminated.To realize high precision voltage measurement for Pt-resistance and reference resist-ance,a time-sharing voltage acquisition unit with high precision and quick step response was also designed.Experimental results show that the high precision Pt-resistance temperature measurement system can achieve the stability of 0.005℃/10day,the resolution of 0.005℃and the accuracy of 0.02 ℃(k=2).It meets the requirements of high accuracy temperature measurement in ultra-precision laser interferometers.

The Preparation and Properties Study of the Zirconia Dispersion-Strengthened Platinum Materials

s: The zirconia dispersion-strengthened platinum thermocouple materials were successfully fabricated by powder metallurgic method. It was studied the zirconia grains influences on platinum materials. The results of the study show that its density is 21.4g/cm3 and its relative density is 99.8%. Its tensile strength obvious overtop pure platinum, the maximum tensile strength is 930MPa. The cures of tensile strength with the processing rate improved of the materials obey a analogy-linear law. The resistance ratio (R100/R0)1.3922, and thermal electromotive force of Pt matched PtRh10 meet I measuring accuracy grade relative to GB/T1598-2010 stander.

FILM THICKNESS INFLUENCES ON THE THERMOELECTRIC PROPERTIES OF NiCr/NiSi THIN FILM THERMOCOUPLES

NiCr / NiSi thin film thermocouples (TFTCs) with a multi-layer structure were fabricated on Ni -based superalloy substrates (95 mm × 35 mm × 2 mm) by magnetron sputtering and electron beam evaporation. The five-layer structure is composed of NiCrAlY buffer layer (2 μm), thermally grown Al 2 O 3 bond layer (200 nm), Al 2 O 3 insulating layer (10 μm), NiCr / NiSi TFTCs (1 μm), and Al 2 O 3 protective layer (500 nm). Influences of thermocouple layer thickness on thermoelectric properties were investigated. Seebeck coefficient of the samples with the increase in thermocouple layer thickness from 0.5 μm to 1 μm increased from 27.8 μV/°C to 33.8 μV/°C, but exhibited almost no change with further increase in thermocouple layer thickness from 1 μm to 2 μm. Dependence on temperature of the thermal electromotive force of the samples almost followed standard thermocouple characteristic curves when the thickness of the thermocouple layer was 1 μm and 2 μm. Sensitive coefficient K of the samples increased greatly with the increase in thickness of the thermocouple layer from 0.5 μm to 1 μm, but decreased insignificantly with the increase in thermocouple layer thickness from 1 μm to 2 μm, and continuously decreased with the increase in temperature. The sensitive coefficient and the stability of NiCr / NiSi TFTCs were both improved after annealing at 600°C.

Thermal electromotive force of hot carriers in γ-irradiated single crystals of cadmium mercury tellurides

The effect of γ-irradiation on the thermal electromotive force (emf) of hot carriers in Cd x Hg1 − x Te (0.25 ≤ x ≤ 0.95) single crystals has been investigated in weak and strong electric fields. It has been shown that in relatively low fields in which the charge carriers are still warm, the relationship |U T | ∼ E 2 is observed because of the dominance of scattering by acoustic vibrations of the lattice with the increasing electric field strength, whereas the dependence of |U T | on E turns to be linear with a further increase of the electric field when the charge carriers become hot. The thermal emf retains its sign in the γ-irradiated crystals. However, there are significant changes in pattern of the field and temperature dependences of |U T |, with the dependence of |U T on E being nonmonotonic at high doses.

A very low thermal EMF computer-controlled scanner

A very low thermal electromotive force (EMF) scanner was designed in our laboratory five years ago. The device was developed to automatically calibrate up to 12 Zener-based voltage standards by comparison to a programmable Josephson voltage standard, but can be used in any set-up that requires automation to set electrical contacts with a repeatability of the thermal EMFs at the nanovolt level. This paper explains how this device achieves robustness of metrological characteristics even after several thousand connections since its first installation. One scanner position shows a voltage offset of 60 nV with a standard deviation of 7 nV while the remaining 11 show offset values between −15 nV and +25 nV with an associated Type A uncertainty varying from 2 to 7 nV. Herein, we present the results of a series of measurements on all channels. Sub-nanovolt residual thermal short EMF variations are demonstrated using Allan variance statistical analysis.

Theory of Seebeck Coefficient in Multi-Walled Carbon Nanotubes

Based on the idea that different temperatures generate different conduction electron densities and the resulting carrier diffusion generates the thermal electromotive force (emf), a new formula for the Seebeck coefficient (thermopower) S is obtained: S=(2/3)ln2(qn)-1εFkBD0, where kB is the Boltzmann constant, and q, n, εF, D0 are charge, carrier density, Fermi energy, density of states at εF, respectively. Ohmic and Seebeck currents are fundamentally different in nature, and hence, cause significantly different behaviors. For example, the Seebeck coefficient S in copper (Cu) is positive, while the Hall coefficient is negative. In general, the Einstein relation between the conductivity and the diffusion coefficient does not hold for a multicarrier metal. Multi-walled carbon nanotubes are superconductors. The Seebeck coefficient S is shown to be proportional to the temperature T above the superconducting temperature Tc based on the model of Cooper pairs as carriers. The S follows a temperature behavior, , where Tg ’= constant, at the lowest temperatures.

The size-dependent thermoelectric response of tungsten-constantan thermocouple in the sub-micro scale

We present the behavior of the thermoelectric response in a nanoscale tungsten-constantan (Cu 58%, Ni 42%) thermocouple (TC). The TC is tip-section typed and fabricated by the stepping method. The thermal electromotive force (emf) showed nearly linear behavior versus temperature over the range from 0 to 100∘C. For the thermocouples with contact radius below 300 nm, the Seebeck coefficient decreased with the size of thermocouples turning smaller. According to the theory based on the free-electron model, the size-dependence thermal electric response may be ascribed to the change of electronic property in nanoscale.

Thermal detection of surface plasmons on gold nanohole arrays

We used a thin-film thermocouple to detect the thermal effect of surface plasmons excited in Au nanohole array structures. We found that the thermal electromotive force of Au film with periodic nanohole structures is three times greater than that of a bare Au film for 785-nm laser excitation at a given power. This effect is caused by the resonant excitation of localized surface plasmons in the nanoholes. In addition, we found that the thermal electromotive force (EMF) of the Au film with dumbbell-like nanohole arrays depends strongly on the incident polarization. The thermal EMF is the greatest when the excitation light is polarized perpendicular to the long axis of the dumbbell.

Research on Self-Generated Voltage of Friction Pair in Dry Wear Process

When friction pair contact with each other, self-generated voltage is a macroscopic potential difference manifested in the face of friction pair as a result of the interaction of diversified factor. It is consisted of contact potential between two different materials, thermal electromotive force in the friction process between two different materials, potential difference created by charge change in the contact and abruption process of friction pair and potential difference created by material transfer in the friction process. Self-generated voltage is measured in the paper through measuring system, and then the relation between self-generated voltage and frictional characteristic is analyzed. It is concluded useful to study observation and diagnosis of equipment friction with self-generated voltage signal of metal friction pair.

Investigation of the thermal electromotive force of steels and alloys of different structural grades in electron beam welding

The results of investigations of the thermoelectric properties of steels of different structural grades and also nickel- and cobalt-based alloys are presented. The temperature dependencies of the absolute thermal electromotive force and the thermal electromotive force coefficient of materials are determined.

Analysis on Thermal Electromotive Force of Carbide Tools

Trying to analysis the influence of the instability of carbide tool materials on cutting temperature measurement by natural thermocouples, a series of experiments calibrating the thermal emf properties of tool inserts were carried out with an improved tool-workpiece thermocouple calibration device. Four chosen types of carbide tools were examined to detect their thermal emf on their different cutting edge areas. By calculating and comparing the thermal emf waving range of them, the thermal emf stability of carbide tools and the temperature measurement error lead by it was evaluated. As the experiments result, the influence was confirmed. The thermal emf variation among the cemented carbide tools was detailed by using certain statistics processing to the experiment data.

Investigation of bimetallic joints by the thermal electromotive force (TMF) method

Results of research into the structure and chemical inhomogeneity of bimetallic compounds obtained by explosion welding and arc centrifugal deposit welding, by the thermal e.m.f. method, are covered.