Thermoelectric Power Measurements Research Articles

Annealing Temperature-Dependent Terahertz Thermal-Electrical Conversion Characteristics of Three-Dimensional Microporous Graphene.

Three-dimensional microporous graphene (3DMG) possesses ultrahigh photon absorptivity and excellent photothermal conversion ability and shows great potential in energy storage and photodetection, especially for the not well-explored terahertz (THz) frequency range. Here, we report on the characterization of the THz thermal-electrical conversion properties of 3DMG with different annealing treatments. We observe distinct behavior of bolometric and photothermoelectric responses varying with annealing temperature. Resistance-temperature characteristics and thermoelectric power measurements reveal that marked charge carrier reversal occurs in 3DMG as the annealing temperature changes between 600 and 800 °C, which can be well explained by Fermi-level tuning associated with oxygen functional group evolution. Benefiting from the large specific surface area of 3DMG, it has an extraordinary capability of reaching thermal equilibrium quickly and exhibits a fast photothermal conversion with a time constant of 23 ms. In addition, 3DMG can serve as an ideal absorber to improve the sensitivity of THz detectors and we demonstrate that the responsivity of a carbon nanotube device could be enhanced by 12 times through 3DMG. Our work provides new insight into the physical characteristics of carrier transport and THz thermal-electrical conversion in 3DMG controlled by annealing temperature and opens an avenue for the development of highly efficient graphene-based THz devices.

Films of filled single-wall carbon nanotubes as a new material for high-performance air-sustainable transparent conductive electrodes operating in a wide spectral range.

In this paper we show the advantages of transparent high conductive films based on filled single-wall carbon nanotubes. The nanotubes with internal channels filled with acceptor molecules (copper chloride or iodine) form networks demonstrating significantly improved characteristics. Due to the charge transfer between the nanotubes and filler, the doped-nanotube films exhibit a drop in electrical sheet resistance of an order of magnitude together with a noticeable increase of film transparency in the visible and near-infrared spectral range. The thermoelectric power measurements show a significant improvement of air-stability of the nanotube network in the course of the filling procedure. For the nanotube films with an initial transparency of 87% at 514 nm and electrical sheet resistance of 862 Ohm sq-1 we observed an improvement of transparency up to 91% and a decrease of sheet resistance down to 98 Ohm sq-1. The combination of the nanotube synthesis technique and molecules for encapsulation has been optimized for applications in optoelectronics.

Characterization and Modelling of the Precipitation Sequence of an Al-Mg-Si Alloy with Silicon Excess for the Prediction of the Mechanical Properties during Ageing

The precipitation sequence of an Al-Mg-Si alloy with silicon excess was determined between 150°C and 300°C by combining ThermoElectric Power measurements and Transmission Electron Microscopy observations. From these studies, an experimental Isothermal Transformation Curve could be proposed in the investigated temperature range. After calibration of a model of KWN type allowing the simultaneous precipitation of two types of metastable rod-shaped precipitates to be taken into account, the same type of curve could be obtained and the yield strength evolution of the alloy during isothermal ageing treatments could be predicted.

Study the Annealing Effect on Electrical properties of (As0.5Se0.5) doped With Tellurium

During this work, the study of electrical properties of (As0.5Se0.5 doped with 1%Te) thin films which prepared by thermal vacuum evaporation on glass substrate bases at room temperature with (100±20)nm thickness, deposition rate (1.6nm/s) and study effect of annealing at temperatures (Ta) (348,398 and448)K for (30min) on these properties. The X-ray diffraction pattern showed that all prepared films have amorphous structure. The electrical measurements explain that D.C. conductivity increases as annealing temperature (Ta) increases and all films have two values of activation energy (Ea1) and (Ea2) and found that it decrease when (Ta) increases. From study Hall effect, all samples showed (p-type) and carrier’s concentration (p) increase while it's mobility decreases with increasing of (Ta). From measurements of thermoelectric power showed that the thermal activation energy (Es) smaller than the D.C. conductivity (Ea2) and (Es) decrease as (Ta) increase.

Study the Annealing Effect on Electrical properties of (As0.5Se0.5) doped With Tellurium

During this work, the study of electrical properties of (As0.5Se0.5 doped with 1%Te) thin films which prepared by thermal vacuum evaporation on glass substrate bases at room temperature with (100±20)nm thickness, deposition rate (1.6nm/s) and study effect of annealing at temperatures (Ta) (348,398 and448)K for (30min) on these properties. The X-ray diffraction pattern showed that all prepared films have amorphous structure. The electrical measurements explain that D.C. conductivity increases as annealing temperature (Ta) increases and all films have two values of activation energy (Ea1) and (Ea2) and found that it decrease when (Ta) increases. From study Hall effect, all samples showed (p-type) and carrier’s concentration (p) increase while it's mobility decreases with increasing of (Ta). From measurements of thermoelectric power showed that the thermal activation energy (Es) smaller than the D.C. conductivity (Ea2) and (Es) decrease as (Ta) increase.

Electrical and optical properties of new Pr3+-doped PbWO4 ceramics

Abstract Polycrystalline samples of new scheelite-type tungstates, Pb1−3x xPr2xWO4 with 0.0098 ⩽ x ⩽ 0.20, where denotes cationic vacancies have been successfully prepared by a high-temperature solid-state reaction method using Pr2(WO4)3 and PbWO4 as the starting reactants. The influence of the Pr3+ substitution in the scheelite framework on the structure and optical properties of prepared new ceramic materials has been examined using powder X-ray diffraction method (XRD) and UV-Vis-NIR spectroscopy. The results of dielectric studies of Pb1−3x xPr2xWO4 samples showed both low values of dielectric constant (below 14) and loss tangent (below 0.2). The electrical conductivity and thermoelectric power measurements revealed a low conductivity (∼2 × 10−9 S/m) and the sign change of thermoelectric power around the temperature of 366 K suggesting the p-n transition. These results are discussed in the context of vacancy, acceptor and donor levels as well as the Maxwell-Wagner model.

Passive thermoelectric power monitoring for material characterisation

Monitoring deterioration of material properties is important for assessing the structural integrity of engineering components, as it may indicate susceptibility to damage. This article focusses on the example of thermoelectric power measurements, which are known to be indicative of thermal and irradiation embrittlement and may therefore act as a proxy metric for material integrity. A passive thermoelectric power–monitoring technique is proposed which is suitable for permanent installation on engineering components. In passive measurements, the active perturbation (in this case, the heating required to create a temperature gradient) is replaced by incidental perturbation from the environment. The reduction in the ‘signal’ amplitude associated with relying on incidental perturbations may be compensated by increasing the number of individual measurements, facilitated by the greatly reduced power demand of the passive modality. Experimental studies using a stainless steel tube as a test component demonstrate thermoelectric power accuracy of <0.03 μV/°C is achievable with temperature gradients of the order of 2°C; in many cases of practical importance, this is sufficient to track the anticipated changes in thermoelectric power associated with thermal degradation.

Thermoelectric Method of Plastic Deformation Detection

The paper presents an approach of non-destructive testing of plastic deformation of metals and alloys by measuring the differential thermoelectric power. Using the developed measuring device for this purpose, measurements of thermoelectric power were performed on several types of steels that are used in the manufacture of product pipelines. Incisions were made on the surface of the testes objects, for the purpose of experimental detection of the place of plastic deformation. In the process of stretching, thermoelectric power was measured at and near the place of the proposed plastic deformation. During the process of stretching the sample, the decrease in thermoelectric power measurement occurs almost linearly. The maximum change in the thermoelectric power measurement of the tested object was observe before the rapture discontinuity.

Transport properties of transition-metal doped BiS2-based superconductors

We performed the electrical resistivity and thermoelectric power measurements of the polycrystalline La0.8Ti0.2OBi(S1-xSex)2. The electrical resistivity of La0.8Ti0.2OBi(S0.7Se0.3)2 at room temperature dramatically decreases, and the temperature dependence shows metallic-like behavior. From the electrical resistivity, superconductivity was not observed in La0.8Ti0.2OBi(S1-xSex)2 above 2.8 K. The value of thermoelectric power S(300 K) of La0.8Ti0.2OBiSSe was about -65 μV/K, which is comparable to that of the polycrystalline LaOBiS2. The value of S(300 K) of La0.8Ti0.2OBiS2 was about -115 μV/K. These power factors are relatively smaller than that of the polycrystalline LaOBiSSe.

Crystallization kinetics study of melt-spun Zr66.7Ni33.3 amorphous alloy by electrical resistivity measurements

In this paper, the electronic transport properties of as-spun Zr66.7Ni33.3 alloys were studied in detail by a combination of electrical resistivity and absolute thermoelectric power measurements over a temperature range from 25 up to 400 °C. Moreover, the isochronal and isothermal crystallization kinetics of Zr66.7Ni33.3 glassy alloy has been investigated based on the electrical resistivity measurements. The comparative study of the crystallization kinetics of these binary amorphous alloys was carried out, for the first time to our knowledge, using an accurate method for electrical resistivity measurements. In the isochronal heating process, the apparent activation energy for crystallization was determined to be, respectively, 371.4 kJ mol−1 and 382.2 kJ mol−1, by means of Kissinger and Ozawa methods. The Johnson–Mehl–Avrami model was used to describe the isothermal transformation kinetics, and the local Avrami exponent has been determined in the range from 2.97 to 3.23 with an average value of 3.1, implying a mainly diffusion-controlled three-dimensional growth with an increasing nucleation rate. Based on an Arrhenius relationship, the local activation energy was analyzed, which yields an average value Ex = 376.2 kJ mol−1.

Study of the Precipitation Process in Aging Steel Pipeline Weldments by Thermoelectric Power Means

The microstructural changes due to the aging process in steel pipeline weldments as a function of the thermoelectric power (TEP) were studied. In general, the thermoelectric methods are based on the well-known Seebeck effect. The thermoelectric methods monitor the TEP via an electron flux induced by a temperature gradient in metallic materials, which is affected by the different types of defects that are present in the atomic lattice, such as atoms in the solid solution, precipitates and dislocations. In this present study, the relationship among the TEP data, hardness and the microstructure of steel pipeline weldments was investigated. In addition, the coarse and dendritic grain structure of the welding material is extremely and unpredictably anisotropic. Such microstructures are no longer direction-independent to the electron flux. Therefore, it has an opposite negative effect on the TEP and overlaps the precipitation effect due to the aging process. TEP and hardness measurements were obtained in each zone of the weldments. For each section of the weldment, the weld bead (WB), heat affected zone (HAZ) and base metal (BM) were found to correspond to particular values of TEP. The relationship between the TEP and the microstructure of a weldment of X60 and X65 micro-alloyed steel that was artificially aged was obtained using the conventional contact TEP technique (hot-tip) and scanning electron microscopy (SEM). It was found that thermoelectric power is very sensitive to the aging process in the two-studied steel pipeline weldments.

Over-ageing of an Al-Mg-Si alloy with silicon excess

The over-ageing of an Al-Mg-Si alloy with Silicon excess was investigated using global thermoelectric power (TEP) and hardness measurements combined with local techniques (Transmission Electron Microscopy (TEM) and Atom Probe Tomography (APT)), in order to highlight how the peak-aged microstructure obtained by a T6 treatment evolves in use conditions at temperatures between 100 °C and 350 °C, leading to a progressive loss of mechanical strength. First, TEP was found to be relevant to study the over-ageing kinetics of the alloy due to its perfect correlation with hardness and its sensitivity to the microstructural changes occurring after peak hardness. Then, APT and TEM observations clearly showed that over-ageing is due to the progressive replacement of the β″ phase by a succession of different types of semi-coherent phases (firstly, of Type B and then of Type A and Type C) and by an extensive precipitation of pure silicon particles. At the highest temperature (T = 350 °C), it was highlighted that the influence of manganese cannot be neglected. From these studies, an experimental Isothermal Transformation Curve could be proposed in the investigated temperature range. Lastly, the decrease in mechanical strength taking place during isothermal and non-isothermal ageing from a T6 state was experimentally characterised and successfully analysed using the JMAK formalism.

β”-(CNB-EDT-TTF)4BF4; Anion Disorder Effects in Bilayer Molecular Metals

The preparation and characterization of new salts based on the dissymmetrical TTF derivative CNB-EDT-TTF (cyanobenzene-ethylenedithio-tetrathiafulvalene) and BF4− anions, are reported. Depending on the electrocrystallization conditions salts with different stoichiometries, (CNB-EDT-TTF)BF4 and β”-(CNB-EDT-TTF)4BF4, can be obtained. The 1:1 salt is an electrical insulator isostructural to the ClO4 analogue previously described. The 4:1 salt is a new member of the family of 2D metals of this donor with different small anions X, (CNB-EDT-TTF)4X, characterized by a bilayer arrangement of the donors and it was obtained in a monoclinic polymorph with a β”-type donor packing pattern. The small anions in this compound are severely disordered between the donor bilayers, which present slightly larger lattice parameters than the isostructural ClO4 analogue. Both electrical conductivity and thermoelectric power measurements in single crystals denote metallic properties as predicted by electronic band structure calculations. As a consequence of the anion disorder the metallic regime of the electrical conductivity denotes electronic localization effects with a progressive increase of resistivity below ~25 K. Because of the larger lattice parameters the intermolecular interactions and electronic bandwidth are decreased compared to other (CNB-EDT-TTF)4X salts. The large and positive thermoelectric power S of this compound (~110 μV/K in the range 100–330 K) and its electrical conductivity σ = 20 S/cm at room temperature lead to a power factor S2σ = 24 μW/K2m, quite large among molecular conductors, placing these compounds as potential candidates for thermoelectric materials.

Field-effect-dependent thermoelectric power in highly resistive Sb2Se3 single nanowire

In this paper, we report the results of our experiments on and measurements of electrical resistivity and thermoelectric power (Seebeck coefficient) from single-crystalline antimony triselenide (Sb2Se3) single nanowires (NWs) with high resistivity (σ ~ 4.37 × 10−4 S/m). A positive Seebeck coefficient of approximately 661 µV/K at room temperature was obtained using a custom-made thermoelectric power probe with an alternating current lock-in method (the 2ω technique), which indicates that the thermal transport is dominated by holes. The measured Seebeck coefficient of the NWs is a factor of 2–3 lower than their bulk counterparts and is comparable to that of a highly conductive Sb2Se3 single NWs (approximately − 750 µV/K). We observed an increase in the Seebeck coefficients with increased bias voltages by field-effect gating, which cannot be explained by the modulation of the Fermi level in the NWs.

Thermopower and magnetocaloric properties in NdSrMnO/CrO3 composites

The thermoelectric power (TEP) and magnetocaloric effect (MCE) for (Nd0.6Sr0.4MnO3)1-x/(CrO3)x composites have been measured. The TEP measurements show a negative sign value of the Seebeck coefficient (S), in microvolts. TEP data construe in the low range of temperature by the magnon and phonon drag model, whereas at high temperature by small polaron conduction mechanism. Magnetic measurements exhibit that all composites show a paramagnetic–ferromagnetic transition with decreasing temperature. The Arrott plots of composites reveal the occurrence of a second order phase transition. The maximum value of magnetic entropy change (ΔS) is 2.37 J kg−1 K−1, achieved fore the composite with x = 0.015. Moreover, the maximum value of relative cooling power (RCP) is 122.1 J kg−1, achieved for the composite with x = 0.020. These composites may be appropriate for magnetic application near room temperature.

Improved thermoelectric power measurements using a four-point technique

The Seebeck coefficient of a material is dependent on its composition and microstructure and is consequently sensitive to service related material degradation; of particular interest is the sensitivity to thermal and irradiation embrittlement which may be exploited for the material characterisation of in service components. Conventionally, thermoelectric measurements are taken using a two-point contact technique which introduces a temperature differential in the test component through a heated ‘hot tip’ electrode; it is argued that measurements using this methodology are sensitive to the thermal contact resistance between the component and the electrodes. An alternative three- or four-point technique is proposed where heat is introduced to the component remotely which leads to much less sensitivity to contact condition. An experiment is presented that compares the two techniques and demonstrates the improved performance of the four-point technique. Aside from the improved accuracy, the modified technique also facilitates a ‘passive’ implementation that could be used from continuous monitoring of components in service.

Polaronic Nonmetal–Correlated Metal Crossover System β′-CuxV2O5 with Anharmonic Copper Oscillation and Thermoelectric Conversion Performance

The crystal structures and electronic properties of β′CuxV2O5 are explored through measurements of X-ray four-circle diffraction, electrical resistivity, thermoelectric power, thermal conductivity, magnetization, and electron paramagnetic resonance. For various compositions with 0.243 ≤ x ≤ 0.587, the crystal structures are redetermined through the anharmonic approach of the copper displacement factors, where the anharmonicity is reduced with increasing Cu concentration. The electron transport for x ≤ 0.45 is nonmetallic due to polaron hopping and the random potential of Cu ions, while for x = 0.60, a correlated Fermi-liquid state appears with a Wilson ratio of 1.3 and a Kadowaki–Woods ratio close to the universal value for heavy-fermion systems. At around x = 0.50, the polaronic bandwidth may broaden so that the Hubbard subbands caused by the electron correlation will overlap. The nonmetallic composition in the proximity of the nonmetal–metal crossover shows a dimensionless thermoelectric power factor of...

Chemical synthesis and characterization of nano-sized rare-earth ruthenium pyrochlore compounds $$\hbox {Ln}_{2}\hbox {Ru}_{2}\hbox {O}_{7}$$ Ln 2 Ru 2 O 7 (Ln = rare earth)

The rare-earth ruthenium pyrochlores $$\hbox {Ln}_{2}\hbox {Ru}_{2}\hbox {O}_{7}$$ ( $$\hbox {Ln} = \hbox {La}^{3+}$$ , $$\hbox {Pr}^{3+}$$ , $$\hbox {Nd}^{3+}$$ , $$\hbox {Sm}^{3+}$$ and $$\hbox {Gd}^{3+}$$ ) have been synthesized by the tartrate co-precipitation method, which allowed control of their composition and morphology. The preparation processes were monitored by thermal studies (TG-DTA). The obtained ruthenates were characterized by X-ray diffraction (XRD), TEM, d.c. electrical conductivity, thermoelectric power and dielectric constant measurements. X-ray diffraction patterns for all pyrochlore samples indicate a single-phase crystalline material with a cubic structure except for $$\hbox {LaRuO}_{3}$$ , which shows perovskite orthorhombic structure. The structural parameter for the solid obtained was successfully determined by Rietveld refinement based on the analysis of powder XRD pattern. The TEM photographs of these compounds exhibited the average particle size in the range of 36.4–73.8 nm. The data on the temperature variation of d.c. electrical conductivity showed that all rare-earth ruthanates are semiconductors and major carriers are electrons. The conduction mechanism of these compounds seems to be oxygen non-stoichiometry. The variation of dielectric constant at various frequencies showed initially interfacial polarization up to 275 kHz and beyond, which shows domain wall motion.

Oxygen vacancy doping of hematite analyzed by electrical conductivity and thermoelectric power measurements

Native defect doping offers an easy and low-cost way of tuning the electrical transport properties of semiconducting binary metal oxides for application in future energy conversion devices. For the first time, the electrical conductivity, charge carrier density, and carrier mobility of hematite in the form of both compact thin films, as well as porous nanoparticle layers, were determined simultaneously with the stepwise introduction of oxygen vacancies. Furthermore, the authors find a drastically reduced phase transition temperature from hematite into magnetite at 620 K, which is up to 380 K lower than values found in the literature.

Temperature dependence of the electrical resistivity and absolute thermoelectric power of amorphous metallic glass Ni33.3Zr66.7

Electron transport properties and thermal stability of Ni33.3Zr66.7 metallic glass (MG) have been studied using an original device for simultaneous measurements of electrical resistivity and absolute thermoelectric power (ATP) controlled by a LabView software written by one of us. The electrical resistivity and absolute thermoelectric power were measured simultaneously and very accurately over a temperature range from 25 to 400°C with a nominal heating rate of 0.5K min−1. The electronic thermal conductivity was also determined using the Wiedemann–Franz law in the same temperature range. Due to its high efficiency, this technique is more and more used because it is characterized by a high sensitivity to detection of the phase transitions related to electronic transport, which is the aim of this study. Analysis of the temperature dependence of the resistivity and ATP of the Ni33.3Zr66.7 glassy ribbons proves the potential of this characterization method to study the thermal behavior of metallic glasses. The crystal structure and the morphology of Ni33.3Zr66.7 metallic glass in the as-quenched state and after heat treatments were studied using X-ray diffraction (XRD), and scanning electron microscope (SEM).