Dimensionless figure of merit and its efficiency estimation for transient response of thermoelectric module based on impedance spectroscopy

Otsuka, Mioko; Hasegawa, Yasuhiro; Arisaka, Taichi; Shinozaki, Ryota; Morita, Hiroyuki

doi:10.7567/apex.10.115801

Cited by 9 publications

(5 citation statements)

References 16 publications

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“…7,9 After an analysis of the frequency dependence of the impedance by a Nyquist diagram, the thermoelectric module is assumed to be a circuit possessing two resistances (R ohm and R TE ) and one capacitance (C TE ), 4,6,7,9 which are a sort of time lag of a first-order circuit. 12 We have introduced a suitable assumption for the module called the RC approximation such that the MEI term in Eq. (1) vanishes.…”

Section: Introductionmentioning

confidence: 99%

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Temperature dependence of dimensionless figure of merit of a thermoelectric module estimated by impedance spectroscopy

Hasegawa

Otsuka

2018

AIP Advances

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Temperature dependence of dimensionless figure of merit zT of a Π-shaped thermoelectric module using bismuth-telluride materials was estimated on the basis of a theory of impedance spectroscopy, which is able to ascertain zT directly using only electrometric measurements from the frequency dependence of the impedance without any calorific measurement. The dependence of the module was measured from 5 mHz to 10 kHz with precise temperature control. From the analysis, the ohmic resistance, the impedance due to the Peltier effect, and the characteristic heat frequency at 300 K were determined under two different boundary conditions (the suspended and fixed conditions of a heat bath). A comparison between these boundary conditions revealed that their difference led to a slight change in the frequency dependence of the measured impedance due to the variation in the heat capacity of the module, and the estimated dimensionless figure of merit was identical for the two boundary conditions (zT ≈ 0.839 at 300 K). The temperature dependence of the dimensionless figure of merit of the module was successfully measured from 20 K to 300 K. The dependence of the thermal conductivity was also estimated with an assumed Seebeck coefficient from the definition of zT. In addition, a new method using only two impedances with repeatability was proposed and demonstrated to estimate the dimensionless figure of merit precisely (zT ≈ 0.845 at 300 K).

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Section: Introductionmentioning

confidence: 99%

“…Using impedance spectroscopy and the RC approximation for the module, Eq. (1) can express the current (or heat) frequency dependence as 7,9,12 …”

Section: Introductionmentioning

confidence: 99%

Temperature dependence of dimensionless figure of merit of a thermoelectric module estimated by impedance spectroscopy

Hasegawa

Otsuka

2018

AIP Advances

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“…2) A few methods using one sample have been proposed to estimate zT directly; the Harman and impedance spectroscopy (IS) methods are representative methods that employ this approach, wherein the Peltier heat Q P (= STI or STi ω , where I and i ω are the direct and alternating currents, respectively) is driven as a probe into the thermoelectric material with the current and can produce a temperature difference along the current direction. [3][4][5][6][7][8][9][10][11][12][13] Consequently, zT is estimated based on the Ohmic resistance and an additional resistance as a thermoelectric resistance, owing to the Peltier heat or temperature difference. Analyzing the model based on the non-steady-state heat equation, both methods are found to be identical in the time and frequency domains.…”

Section: Introductionmentioning

confidence: 99%

Influence of contact resistance and heat leakage in the determination of the dimensionless figure of merit via duo-impedance spectroscopy

Hirabayashi

Hasegawa

2021

Jpn. J. Appl. Phys.

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The influence of contact resistance between a polycrystalline bismuth as a basic thermoelectric material and electrodes made of copper using binders of Ag epoxy and conventional solder was investigated to estimate the dimensionless figure of merit (zT) via impedance spectroscopy (IS). The frequency dependence of the impedance using both binders was measured at 300 K under an appropriate alternating current because a considerably larger Peltier heat was required, relative to Joule heat, for estimating the zT precisely. Through the duo-IS method, zT at 300 K was estimated to be 0.126 ± 0.004 and 0.130 ± 0.002 using the Ag epoxy and solder, respectively. The temperature dependence of zT from 300 to 30 K was also estimated, and zT > 0.01 was a practical based on this technique, owing to its signal–noise ratio. The duo-IS method is invaluable for estimating zT in the entire temperature region based on an appropriate configuration.

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“…To characterize thermoelectric devices, Harman's method and power output measurements have been widely used to evaluate the ZT values and thermoelectric power, respectively, but additional extensive measurements are necessary to determine the three key parameters ( , S, and ). Recently, several studies have demonstrated that impedance spectroscopy can be used to determine the ZT values of thermoelectric bismuth telluride [29] and SKD [30,31] materials as well as bismuth telluride [32][33][34][35][36][37][38] and SKD [39,40] based devices. In a typical galvanostatic impedance spectroscopy measurement, a sinusoidal current perturbation drives the thermoelectric system slightly out of temperature equilibrium (appearance of a temperature gradient), inducing reorganization of the carriers owing to the Peltier effect, which allows the Seebeck voltage to be measured as a function of frequency.…”

Section: Introductionmentioning

confidence: 99%

“…Most investigations using impedance spectroscopy for the characterization of bismuth telluride [29,32,34,35,38] and SKD [39,40] based thermoelectric devices have been performed at ambient temperature, with only a few studies reporting the properties of bismuth telluride based devices at operating temperatures up to 150 °C [33,37]. In this work, we employed impedance spectroscopy to elucidate the thermoelectric properties of an in-house-fabricated two-couple SKD-based device within the range of practical operating temperatures (23-450 °C) with the help of state-of-the-art mathematical models along with electrical, thermal, and microstructural characterization.…”

Section: Introductionmentioning

confidence: 99%

Determination of the thermoelectric properties of a skutterudite-based device at practical operating temperatures by impedance spectroscopy

et al. 2019

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Skutterudite-based thermoelectric materials are promising candidates for waste heat recovery applications at intermediate temperatures (300-500 °C) owing to their high dimensionless figure of merit and power factor. Recently, several researchers have reported the high performance of skutterudite-based thermoelectric devices obtained by optimizing the crystal structure and microstructure of skutterudite materials and developing metallization layers for device fabrication. Despite extensive research efforts toward maximizing the power density and thermoelectric conversion efficiency of skutterudite-based devices, the thermoelectric properties of such devices after fabrication remain largely unknown. Here, we systematically investigated the factors that affect the thermoelectric properties of skutterudite-based devices within the range of practical operating temperatures (23-450 °C). We successfully prepared a two-couple skutterudite-based device with titanium metallization layers on both sides of the thermoelectric legs and characterized it using scanning and transmission electron microscopy and specific contact resistance measurements. Impedance spectroscopy measurements of the two-couple skutterudite-based device revealed the figure of merit of the device and enabled the extraction of three key thermoelectric parameters (Seebeck coefficient, thermal conductivity, and electrical conductivity). The impedance spectra and extracted parameters depended strongly on the measurement temperature and were mainly attributable to the thermoelectric properties of skutterudite materials. These observations demonstrate the interplay between the properties of thermoelectric materials and devices and can aid in directing future research on thermoelectric device fabrication.

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Dimensionless figure of merit and its efficiency estimation for transient response of thermoelectric module based on impedance spectroscopy

Cited by 9 publications

References 16 publications

Temperature dependence of dimensionless figure of merit of a thermoelectric module estimated by impedance spectroscopy

Temperature dependence of dimensionless figure of merit of a thermoelectric module estimated by impedance spectroscopy

Influence of contact resistance and heat leakage in the determination of the dimensionless figure of merit via duo-impedance spectroscopy

Determination of the thermoelectric properties of a skutterudite-based device at practical operating temperatures by impedance spectroscopy

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