Seebeck Coefficient Measurements Research Articles

Influence of the sheet metal Seebeck coefficient on wear detection based on thermoelectric measurement

The measurement of thermoelectric current is a new and effective method for inline wear detection in sheet metal forming. The measuring principle is based on the Seebeck effect, whose characteristic value, the Seebeck coefficient depends on the material composition. In the previous research of the authors, a boundary value of the thermoelectric value that separates the mild and severe wear was identified. Due to the large deviation of the Seebeck coefficient of the material used in sheet metal forming, it is worth discussing the influence of the Seebeck coefficient of the sheet metal material on the effectiveness and boundary value of the thermoelectric current for wear detection. In this paper, the measuring principle is first illustrated using an equation based on thermoelectricity. The Seebeck coefficients of the tools and sheet metals are then determined by a specifically designed device. At the same time, the wear tests for different materials are used to determine the boundary values for different tribological systems. Finally, the obtained Seebeck coefficient and boundary values are compared. From the results it can be concluded that the value of the measured Seebeck coefficients have a discernible effect on the boundary values, which provides a useful insight for inline wear diagnosis for practical applications.

Errors Associated in Seebeck Coefficient Measurement for Thermoelectric Metrology

Accurate and precise measurement with authentic data dispersion can be considered as a prime tool to realize any technologies at large scale. In the context of thermoelectric technology, a combination of Seebeck coefficient (α), electrical conductivity (σ) and thermal conductivity (κ) are prominent physical parameters that dictate the performance of thermoelectric materials. In this review article, we have stressed the attention on accurate and precise measurement of Seebeck coefficient that includes various sources of errors from contact geometry, sensors, measurement techniques and thermocouple. In addition to this, the solution of minimizing the errors associated in Seebeck measurement has also been elaborated.

Versatile Seebeck and electrical resistivity measurement setup for thin films.

A custom setup for Seebeck coefficient and electrical resistivity measurements of thin films as a function of temperature in the range of 10-300K was developed. The Seebeck coefficient is measured using a two-probe arrangement and using either a dynamical or steady/quasi-steady differential method. The temperature differences (ΔTs) for these measurements across the samples are achieved by using resistive heaters embedded in two copper blocks. The sample is screwed to these blocks and is in pressured contact with the measurement probes. The electrical resistivity is measured with a two-probe arrangement. To verify the reliability of the developed setup, measurement tests were performed on commercial niobium foil and a specular spin valve previously studied, having obtained a great accordance (within ∼3%) between this setup's experimental results and the reference measurements.

Simple, reversible gradient Seebeck coefficient measurement system for 300-600K with COMSOL simulations.

Seebeck measurement is a crucial step for characterizing thermoelectric samples, as measuring the accurate value with a simpler system design is challenging. Here, we report a simple design of the Seebeck coefficient measurement system, which can measure the thermo-emf (Seebeck coefficient) of the sample, under a limited temperature range of 300-600K. Unlike the majority of the reported instrumental designs, the system does not have a hot walled chamber. The sample is sandwiched between two brass block supported heaters, which are controlled separately. Thus, this type of system is suitable for a window of the temperature range near room temperature. In this paper, we report the system that can measure the Seebeck coefficient up to 600K. The heaters touch the sample through 1mm thick silver caps, which offer insignificant thermal resistance and a stable temperature, as seen through experiment as well as COMSOL simulations. A typical sample has, at maximum, a diameter of 10mm and a thickness of 2-3mm. A reversible temperature gradient is applied in quasi-static direct current mode. By virtue of its design, the sample holder ensures a minimum thermal and electrical contact resistance during a measurement cycle. The combination of metals used for measurement (Ag and Cu) shows negligible junction contribution. The variance up to ±2% and accuracy up to 8% at a high temperature have been obtained using calibration sample reference data of state-of-the-art commercial systems.

Tunable thermoelectric properties of free-standing PEDOT nanofiber film through adjusting its nanostructure

Recently, organic thermoelectric (TE) materials have attracted increasing attention in green energy conversion. However, researches on polymer nanostructured TE materials are still scarce, especially for the 1 D nanostructured polymer materials. In this work, 1D poly(3,4-ethylenedioxythiophene) (PEDOT) nanofiber was synthesized by a self-assembled micellar soft-template approach using anionic surfactant sodium dodecyl sulfate (SDS). Then, a flexible and free-standing PEDOT nanofiber film was prepared through a simple vacuum-assisted filtration method. FE-SEM and TEM characteristics real 1D configuration for all the PEDOT nanostructures. Through adjusting the molar ratio of SDS, oxidizing agent FeCl3 and EDOT monomer (nSDS: nFeCl3: nEDOT), nanofiber with different diameter (10–200 nm) and microtopography can be obtained. Electrical conductivity and Seebeck coefficient measurement indicates that the TE properties of PEDOT can be effectively tuned by adjusting its nanostructure, and a variation range as high as three orders of magnitude for the power factors (10-2–101 μW/mK2) can be realized. Due to a more ordered structure caused by the edge-on packing mode of PEDOT chain, the sample prepared with nSDS: nFeCl3: nEDOT = 30:15:7 shows the highest power factor of 7.2 μW/mK2. This value can be further enhanced to 14.4 μW/mK2 by constructing PEDOT nanofiber/SWCNTs composite.

Thermoelectric transport properties of the van der Waals-type layered rhombohedral SnAs-based compound, EuSn2As2

The thermoelectric transport properties of the van der Waals-type layered rhombohedral SnAs-based compound, EuSn2As2, have been investigated. A densified polycrystalline sample of EuSn2As2 with porosity (ϕ) of 2.4(9) vol.% exhibited a weak orientation to the c-axis for hexagonal coordination system; the weak orientation is parallel (P ∥) to the pressing direction of hot pressing. Measurements of electrical resistivity (ρ), Seebeck coefficient (S), and thermal conductivity (κ) were conducted perpendicular (P ⊥) to the pressing direction. The experimental values of ρ and S exhibit metallic temperature dependence and p-type carrier polarity. The power factor (P) was 0.51(8) mW m−1 K−2 at 673(4) K. Using the Wiedemann–Franz–Lorenz law, the phonon thermal conductivity (κ ph) was estimated to be 0.4(6) W m−1 K−1 at 673(6) K. The dimensionless figure of merit, ZT, was 0.092(17) at 673(3) K.

The influence of Fe2O3 reagent grade purity on the electrical properties of ‘undoped’ LaFeO3 ceramics: A cautionary reminder

Low levels of impurities can have a dramatic influence on the electrical properties of metal oxides. Here, we use a combination of impedance spectroscopy and Seebeck coefficient measurements to show the defect chemistry and p-type conduction mechanism in undoped LaFeO3(LF) ceramics is significantly influenced by impurities in Fe2O3 reagents. A low but significant concentration of impurities associated with 99.9 % Fe2O3 reagent is sufficient to compete against the intrinsic Schottky disorder responsible for the p-type behaviour normally observed for undoped LF ceramics. This produces electrically heterogeneous grain (bulk) responses that are strongly dependent on the processing conditions. To achieve electrically homogeneous bulk responses requires adjustment of the oxygen content by annealing in a reducing atmosphere (n-type) or via doping with a significant level of acceptors (mixed ionic/ p-type electronic). These results illustrate the importance of using high purity reagents when studying the electrical properties of ferrite-based perovskites.

Wide range temperature-dependent (80–630 K) study of Hall effect and the Seebeck coefficient of β -Ga2O3 single crystals

Investigation of the Seebeck coefficient in ultra-wide bandgap materials presents a challenge in measurements; nevertheless, it is essential for understanding fundamental transport mechanisms involved in electrical and thermal conduction. β-Ga2O3 is a strategic material for high-power optoelectronic applications. The present work reports the Seebeck coefficient measurement for single crystal Sn-doped β-Ga2O3 in a wide temperature range (80–630 K). The non-monotonic trend with large magnitude and a negative sign in the entire temperature range shows that electrons are dominant carriers. The structural and Raman characterization confirms the single-phase and the presence of low-, mid-, and high-frequency phonon modes, respectively. The temperature-dependent (90–350 K) Hall effect measurement was carried out as a supplementary study. Hall mobility showed that μ ∝ T1.12 for T < 135 K and μ ∝ T−0.70 for T > 220 K. Activation energies from the Seebeck coefficient and conductivity analysis revealed the presence of interband conduction due to impurity defects. The room temperature Seebeck coefficient, power factor, and thermal conductivity were found to be 68.57 ± 1.27 μV/K, 0.15 ± 0.04 μW/K2 cm, and 14.2 ± 0.6 W/mK, respectively. The value of the figure of merit for β-Ga2O3 was found to be ∼ 0.01 (300 K).

Morphological Analysis and Properties Evaluation of Electrodeposited Thick BiSbTe Films with Cooperative Interactions among Multiple Additives

As a cost-effective method, electrodeposition has been widely applied to synthesize materials for the fabrication of micro thermoelectric devices. However, it is hard to obtain smooth, compact and high-performance p-type BiSbTe films when the thickness becomes higher. In this work, multiple additives consist of PVA and saccharin sodium are firstly introduced into the electrolyte bath with the assistance of KCl for electrodeposition. The influence of different additives on reduction kinetics, morphology, stoichiometry and crystalline structure has been thoroughly explored. Besides the electrolyte concentration and the deposition potential, the pulse duration for pulsed deposition also significantly affects the stoichiometry. The smooth, compact and well-adherent films with ideal composition were successfully deposited for the thickness range from 4 to 100 μm. Crystallite size was much refined, and lattice strain slightly increased with the cooperative reaction of multiple additives. The measured Seebeck coefficient reached around 262 ± 25 μV K−1 for the deposited film with multiple additives, while that of the film with absence of additives was about 156 ± 14 μV K−1. The electric resistivity increased from 66 μΩ·m to 150 μΩ·m when PVA and saccharin sodium were introduced, but decreased to 81 μΩ·m after increasing the electrolyte conductivity through adding KCl.

The Effect of Crystal Mismatch on the Thermoelectric Performance Enhancement of Nano Cu2Se

In the past decades, Cu2−xSe compounds have attracted great attention due to the inclusion of non-toxic and abundant elements, besides having a promising thermoelectric (TE) performance. In this work, we investigated the effect of a crystal mismatch of a nanoinclusion phase on the TE properties of Cu2−xSe. Nano-Cu2Se was synthesized using microwave assisted thermolysis, while the p-type skutterudite, Fe3.25Co0.75Sb12 (FeCoSb), compound was synthesized using a chemical alloying route. Nano-Cu2Se, and (nano-Cu2Se)1−x(nano-FeCoSb)x composites, where x = 0.05 and 0.1, were prepared via mechanical alloying followed by Spark Plasma Sintering process. Structural properties were evaluated by PXRD and SEM analysis, while the high temperature transport properties were examined via electrical conductivity, Seebeck coefficient, and thermal conductivity measurements in the temperature range of 300–800 K. Powder X-ray diffraction (PXRD) confirmed a single phase of nano Cu2Se, while the samples with FeCoSb inclusion consist of two phases as Cu2Se and CoSb3. SEM micrographs of all samples show that Cu2Se has randomly oriented grains with different sizes. Cu2Se samples with a FeCoSb inclusion show a rather different structure. In these samples, a rod-shaped FeCoSb phase, with a size varying between 20 and 100 nm, showed an inhomogeneous distribution in the structure and stacked between the Cu2Se layers. Transport data indicate that crystal mismatch between Cu2Se and FeCoSb has a strong effect on the TE transport properties. Electrical conductivity decreases but Seebeck coefficient enhances with nano FeCoSb inclusion. Total thermal conductivity was suppressed by 30% and ZT value enhanced by 15% with 5% nano FeCoSb inclusion at 750 K, likely due to a decrease in the electronic contribution of the thermal conductivity. Structural and transport data show that small amount of nanoinclusion of FeCoSb has a beneficial effect on the TE performance of nano Cu2Se at temperatures below 800 K.

Single crystal growth and characterization of new Zintl phase Ca9Zn3.1In0.9Sb9

Complex Zintl phases have yielded a large variety of promising new thermoelectric materials. In this study we report the discovery of the new Zintl phase Ca9(Zn1–xInx)4Sb9 (x ​~ ​0.9), needle-like crystals of which were serendipitously obtained from an In- and Sb-rich flux. Although its composition is reminiscent of Ca9Zn4+xSb9, an excellent thermoelectric material with zT ​> ​1, the substitution of In on the Zn site leads to the formation of an entirely new structure type. Single crystal X-ray diffraction revealed a structure characterized by TSb4 tetrahedra (T ​= ​statistically disordered Zn and In atoms) and ZnSb3 triangular units, which share common corners to form [T4Sb9]18− polyanions. The average structure was found to have hexagonal symmetry. The valence electron count in this heavily-disordered structure appears to follows the Zintl-Klemm rules, suggesting semiconducting behavior. Single crystal electrical conductivity and Seebeck coefficient measurements support this conclusion, suggesting that the as-grown crystals are degenerate p-type semiconductors.

N-type charge transport in heavily p-doped polymers.

It is commonly assumed that charge-carrier transport in doped π-conjugated polymers is dominated by one type of charge carrier, either holes or electrons, as determined by the chemistry of the dopant. Here, through Seebeck coefficient and Hall effect measurements, we show that mobile electrons contribute substantially to charge-carrier transport in π-conjugated polymers that are heavily p-doped with strong electron acceptors. Specifically, the Seebeck coefficient of several p-doped polymers changes sign from positive to negative as the concentration of the oxidizing agents FeCl3 or NOBF4 increase, and Hall effect measurements for the same p-doped polymers reveal that electrons become the dominant delocalized charge carriers. Ultraviolet and inverse photoelectron spectroscopy measurements show that doping with oxidizing agents results in elimination of the transport gap at high doping concentrations. This approach of heavy p-type doping is demonstrated to provide a promising route to high-performance n-type organic thermoelectric materials.

A Robust System for Thermoelectric Device Characterization

Due to the large reduction in fossil fuel reservoirs, the consequent cost increase of deepwater extraction, and the emission of pollutants, there is a constant search for alternative ways to obtain clean energy at a lower cost. Among those sources, we focus on the energy produced by thermoelectric materials. In this work, we present a new system for the characterization of thermoelectric generation devices. Such a system performs measurements of electrical resistivity, Seebeck coefficient, and thermal conductivity in a single setup. With this, it is possible to reduce the systematic errors in the figure of merit $ZT$ and the cost of the equipment. Our equipment, together with the developed software, presented excellent results and analyses, and with that, it proves to be a robust alternative for the characterization of commercial thermoelectric devices, and of laboratory thin film thermoelectric materials.

Thermopower Enhancement of Rutile-type SnO2 Nanocrystalline Using Facile Co-Precipitation Method

Metal oxide semiconductor has attracted so much attention due to its high carrier mobility. Herein, thermoelectric study of nanocrystalline SnO2 through a simple co-precipitation method is conducted to enhance the Seebeck coefficient (S). X-ray diffraction, thermogravimetric analysis (TGA), resistivity (r), Seebeck coefficient (S), and power factor (PF) measurements are conducted to analyze the thermoelectric properties of the material. The measurements show that there are two interesting results, which are the unusual resistivity behavior and the high value of the S. Resistivity behavior shows a non-reflective intermediate semiconductor-metals behavior where the turning point occurs at 250 o C. This behavior is strongly correlated to the surface oxide reaction due to annealing temperature. The maximum S likely occurs at 250 ºC, since the curve shows a slight thermopower peak at 250 ºC. The value of the S is quite high with around twenty times higher than other publications about SnO2 thermoelectric material, this happens due to the bandgap broadening. The energy gap of SnO2 calculated using density functional theory (DFT), which was performed by Quantum Espresso 6.6. The result shows that there is a broadening energy gap at different momentum or wave factor. Nanocrystalline semiconductors material is giving an impact to increase the width of bandgap due to quantum confinement and could enhance the thermopower especially in SnO2 nanocrystalline

SnOx and a-Si thin-films based photodiode in a flexible substrate for visible spectral region

Thin-films based photodiodes are an advantageous alternative to the photodetectors based on semiconductor doping processes, especially in optical sensors implemented on non-semiconductor substrates. This is the first report of a p-i-n junction photodiode, based on n-SnOx/p-SnOx and amorphous silicon (a-Si) thin-films, fabricated in a polymeric, flexible and photosensitive substrate, only considering different annealing conditions and thicknesses of evaporated metallic Sn and sputtered a-Si. Seebeck coefficient measurements were performed, using a custom-built setup, to assess the implementation of n- and p-type thin-films. The obtained Seebeck coefficients were −167 µV/K and +266 µV/K for the n-SnOx and p-SnOx, respectively. X–ray diffraction (XRD) analysis also confirmed the deposition of an a-Si thin-film as the intrinsic layer of the p-i-n junction. The photodiode responsivity and response times were measured, using a custom-built optical setup for the visible spectral region. The measured responsivity (at 0 V reverse bias) was 2.8µA/W at 572 nm and the rise and fall times were 0.203 s and 0.312 s, respectively. The developed photodiode provides a promising solution for high level light detection applications in flexible optical sensors.

Analysis of the ‘cold finger effect’ in measuring the Seebeck coefficient

This work analysed one of the most important uncertainty contributions in measuring the Seebeck coefficient of thermoelectric materials: the ‘cold finger effect’ (CFE). A didactic approach based on the fundamental laws of thermoelectric circuits is used to explain the influence of this effect on the Seebeck coefficient measured. Finite element simulations and practical measurements of an ISOTAN® sample were performed under different conditions relating to the thermal coupling of the probes to the sample, and the results are presented. Relative errors of the Seebeck coefficient of up to a few percent can occur if measurements are conducted under non-optimum measuring conditions. It is shown how the thermal coupling of the probes to the sample can minimize the influence of the CFE on the measured Seebeck coefficient.

Experimental setup for the Seebeck and Nernst coefficient measurements.

A new experimental setup is designed for the measurement of Seebeck and Nernst coefficients on the single crystal flakes and polycrystalline samples. The setup utilizes the multifunctional probe assembly of the physical property measurement system by Quantum Design, Inc. and can measure in the temperature range of 1.8 K-380 K up to 8 T magnetic fields. The experimental measurement was fully automated through a computer using the code written in LabVIEW software. The setup is capable of measurements on samples as small as 2 × 1 mm2 in size and thickness as small as a few micrometers, which is quite important for the crystal flakes grown using the vapor transport method. The determination of the coefficients is based on the quasi-static approach, with the thermal gradient of 0.2 K-1.2 K across the sample in the measured temperature range of 1.8 K-300 K. The sensitivity of the instrument is better than 0.1 µV/K, and the accuracy is better than ∼0.5 µV/K, which can be further improved with the better quality of electrical contacts on the sample. The Seebeck and Nernst coefficient measurements performed on some well-studied semimetallic (bismuth), thermoelectric (Bi2Se3), and superconducting (FeTe0.5Se0.5) systems are also presented.

A low-cost apparatus to measure the Seebeck coefficient

In this paper, a very simple and low-cost setup design is described for the Seebeck coefficient measurement of the disc and rod-shaped specimens. The setup has been tested for its reliable working by measuring the Seebeck coefficients of standard samples; measured values match with the literature. The setup can be built with commonly available raw materials in a short time. The tool is portable and can be used as a testing tool or to demonstrate the thermoelectric effect in different materials.

Modelling and uncertainty analysis of Seebeck coefficient measurements by using the finite element method

Abstract The present work is focused on the determination of single uncertainty contributions of Seebeck coefficient measurements of semiconducting bulk materials. Different simulations are performed to quantitatively explore effects and their influence on the measurement uncertainty. The following effects are studied by the finite element method (FEM): the choice of data sets from transient thermoelectric signals, the influence of asynchronous voltage and temperature measurements, and the so called “finger” effect, which represents the falsification of a measurement caused by the contact resistance between a sensor and a sample. The FEM allows the exploration of the data space under ideal conditions, which are hardly obtainable in real experiments. The results of the simulations are used to quantify the corresponding uncertainty contributions.

Electronic quality factor for thermoelectrics.

Development of thermoelectrics usually involves trial-and-error investigations, including time-consuming synthesis and measurements. Here, we identify the electronic quality factor BE for determining the maximum thermoelectric power factor, which can be conveniently estimated by a single measurement of Seebeck coefficient and electrical conductivity of only one sample, not necessarily optimized, at an arbitrary temperature. We demonstrate that thousands of experimental measurements in dozens of materials can all be described by a universal curve and a single material parameter BE for each class of materials. Furthermore, any deviation in BE with temperature or doping indicated new effects such as band convergence or additional scattering. This makes BE a powerful tool for evaluating and guiding the development of thermoelectrics. We demonstrate the power of BE to show both p-type GeTe alloys and n-type Mg3SbBi alloys as highly competitive materials, at near room temperature, to state-of-the-art Bi2Te3 alloys used in nearly all commercial applications.