Measurement of Thermal Conductivity by Utilization of the Peltier Effect

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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“…10,11 Later, we will compare the Harman method and impedance spectroscopy. The most important result from impedance spectroscopy in Eqs.…”

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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“…In the present method the temperature difference in the sample is ~100-200mK and the measurements are made near the limit of ∆T~0. Therefore, the expression of Z=α Possibility of the non-linear temperature distribution has been pointed out 4) which is caused by the thermal radiation due to the temperature difference between the heat bath and the heated and cooled ends of the sample induced by the dc current. However, this effect is discarded here because of the same value of ZT obtained in the different temperature difference in our equipment 2) .…”

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confidence: 99%

Non-equilibrium and non-linear stationary states in thermoelectric materials

Iwasaki

Koyano

Yamamura

et al. 2004

Solid State Communications

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Efficiency of thermoelectric materials is characterized by the figure of merit Z. Z has been believed to be a peculiar material constant. However, the accurate measurements in the present work reveal that Z has large size dependence and a non-linear temperature distribution appears as stationary state in the thermoelectric material. The observation of these phenomena is achieved by the Harman method. This method is the most appropriate way to investigate the thermoelectric properties because the dc and ac resistances are measured by the same electrode configuration. W e describe the anomalous thermoelectric properties observed in mainly (Bi,Sb) 2 Te 3 by the Harman method and then insist that Z is not the peculiar material constant but must be defined as the physical quantity dependent of the size and the position in the material.

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“…The Seebeck effect was acquired by applying the temperature gradient in the sample by use of the homemade instrument. The dimensionless figure of merit was measured by the Harman method [2]. The characterization of the sample was performed by the scanning electron microscopy and the energy dispersive X-ray analysis, and the X-ray diffraction.…”

Section: Methodsmentioning

confidence: 99%