Evaluation of a thermoelectric material using duo-frequency impedance spectroscopy method

2020

Appl. Phys. Express

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Commercialized bulk constantan with a low dimensionless figure of merit and its film fabricated by electroplating were prepared to demonstrate the feasibility of impedance spectroscopy for estimating thermoelectric parameters. From the frequency dependence of the impedance, the resistivity and dimensionless figure of merit were directly estimated as 5.3 × 10−7 Ωm and 0.026 for the bulk and 3.8 × 10−7 Ωm and 0.0098 for the film at room temperature (302 K), respectively. We concluded that impedance spectroscopy is a suitable technique for estimating the thermoelectric parameters of any material with an apparent Seebeck coefficient.

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confidence: 99%

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confidence: 99%

Dimensionless figure of merit of constantan estimated using impedance spectroscopy

Shinozaki

Hirabayashi

2020

Appl. Phys. Express

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“…Therefore, Re[ Z mea ( ω )] (∝ I ) increased marginally at 10 –3 Hz owing to Q P (= 6.9 mW) ~ Q J (= 4.8 mW) using the representative magnitude of S (= − 231 μV/K at 300 K) corresponding to BiTe standard material 24 . In addition, ϕ = tan −1 (Im[ Z mea ( ω )]/Re[ Z mea ( ω )]) helps identify the suitable frequency for determining Z mea ( ω → ∞) and Z mea ( ω → 0) because ω R2C is unknown 15 . Finally, using the IS method, the value of zT was clearly estimated as ( zT ) IS = 0.811 (= ( R ohm + R TE ) IS /( R ohm ) IS − 1 = 869.5 / 480.0 − 1).…”

Section: Resultsmentioning

confidence: 99%

“…ω TE is denoted as a function of thermal diffusivity ( α ) and L of the TE, ω TE ∝ α / L 2 , and typically approaches 1 rad/s owing to the small value of κ (∝ α ) of the TEs. Therefore, the angular frequency satisfying Z ( ω → 0) would approximately be of the order of 10 –2 –10 –4 rad/s, depending on L 12 , 15 . The theory and model of the IS method clearly demonstrates that the Harman method is one of the results obtained using Z ( ω → ∞) → R AC and Z ( ω → 0) → R DC from Eq.…”

Section: Introductionmentioning

confidence: 99%

Proposal of time domain impedance spectroscopy to determine precise dimensionless figure of merit for thermoelectric modules within minutes

Takeuchi

2022

Sci Rep

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Several techniques exist that use a thermoelectric element (TE) or module (TM) to measure precise dimensionless figure of merit (zT), both qualitatively and quantitatively. The techniques can be applied using both alternating (AC) and direct current (DC). Herein, the transient Harman (TH) and impedance spectroscopy (IS) methods were investigated as direct zT measurement techniques using identical TM, which showed that zT at 300 K was 0.767 and 0.811 within several minutes and several hours, respectively. The zT values differed despite the use of the same TM, which revealed that measuring ohmic resistance using DC and pulse DC is potentially misleading owing to the influence of Peltier heat on current flow. In this study, time domain impedance spectroscopy (TDIS) was proposed as a new technique to measure zT using proper DC and AC. zT obtained using TDIS was 0.811 within several minutes using the time and frequency domains, and was perfectly consistent with the result of the IS method. In conclusion, the TDIS is highly appropriate in estimating zT directly using only proper electrometric measurements, and without any heat measurements.

“…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

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.