Transport Properties of Bulk Thermoelectrics: An International Round-Robin Study, Part II: Thermal Diffusivity, Specific Heat, and Thermal Conductivity

Wang, Hsin; Porter, Wallace D.; Böttner, H.; König, Jan; Chen, Lidong; Bai, Shengqiang; Tritt, Terry M.; Mayolet, Alex; Senawiratne, J.; Smith, Charlene M.; Harris, Fred R.; Gilbert, Patricia; Sharp, Jeff; Lo, Jason; Kleinke, Holger; Kiss, László I.

doi:10.1007/s11664-013-2516-0

Cited by 140 publications

(108 citation statements)

References 34 publications

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“…Even for routinely conducted measurements by experienced groups, differences in zT can be 20% as found by Hsin Wang et al, 24 and uncertainty increases with temperature. The heat capacity is the largest contribution to the error in thermal conductivity which can be signicantly reduced by comparison to the Dulong-Petit value.…”

Section: Resultsmentioning

confidence: 94%

“…The scatter in thermal diffusivity between different laboratories can be as high as 5% at room temperature and almost 10% at 500 K. 24 Much of this can be ascribed to variations in measured thickness. This indicates that a constant and accurately measured thickness is as important for diffusivity measurements as the geometric factor is for resistivity measurements.…”

Section: 93mentioning

confidence: 99%

“…Heat capacity is the measurement most sensitive to operator error and inexperience. 24 Above the Debye temperature and in the absence of phase transitions, C p normally increases slightly with temperature. The best data quality check is comparison to the Dulong-Petit law which states that the constant volume heat capacity above the Debye temperature is approximately 3k B per atom, or C The measured C p above the Debye temperature should be close to or slightly higher than the Dulong-Petit value and increase slowly with temperature.…”

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confidence: 98%

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Measuring thermoelectric transport properties of materials

Borup

Boor

Wang

et al. 2015

Energy Environ. Sci.

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In this review we discuss considerations regarding the common techniques used for measuring thermoelectric transport properties necessary for calculating the thermoelectric figure of merit, zT.Advice for improving the data quality in Seebeck coefficient, electrical resistivity, and thermal conductivity (from flash diffusivity and heat capacity) measurements are given together with methods for identifying possible erroneous data. Measurement of the Hall coefficient and calculation of the charge carrier concentration and mobility is also included due to its importance for understanding materials. It is not intended to be a complete record or comparison of all the different techniques employed in thermoelectrics. Rather, by providing an overview of common techniques and their inherent difficulties it is an aid to new researchers or students in the field. The focus is mainly on high temperature measurements but low temperature techniques are also briefly discussed. Measurement guide for authors and reviewersMeasurements should always be repeatable on the same sample, and on new samples produced in the manner described. Thermoelectric effects are steady-state effects so any time dependence or hysteresis is indication that phenomena outside thermoelectric effects are at play. Materials with chemical oxidants/ reductants incorporated are likely to contain unstable internal voltages not due to thermoelectric effects. Unconventional samples or measurement methods deserve reexamination of assumptions. AccuracyTrue accuracy is not represented by a single heating curve from one sample, even with error bars representing instrument precision. Showing heating and cooling data and multiple samples gives a better indication of measurement variability for a typical type of sample. Anisotropy, cracks and inhomogeneities can lead to large variation in measurements. One unusual data point or sample outside the trend, particularly at temperatures just prior to decomposition, usually indicates a problem in sample or measurement. Unusual resultsTypical thermoelectric materials behave like heavily doped semiconductors with thermopower (absolute value of Seebeck coefficient) of less than 300 mV K À1 , resistivity of 0.1-10 mU cm, and are optimized when electronic contribution to the thermal conductivity is about 1/2 the total thermal conductivity. Extraordinary results should be checked by extra means. Unusual results can be caused by bad contacts, thermocouples that have broken, chemically reacted, or simply dried out of calibration. Exceptional resultsReported values of zT > 1 or in unexpected materials receive extra attention from reviewers who may ask for additional conrmation. Convincing measurements may need to be performed on the same sample along the same direction and be repeatable with other samples and measurement methods. There is no official record keeping for claimed or veried zT values. Several papers, patents and press releases have claimed extraordinarily high zT but most have been forgotten over time and likely resul...

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Section: Resultsmentioning

confidence: 94%

Section: 93mentioning

confidence: 99%

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confidence: 98%

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Measuring thermoelectric transport properties of materials

Borup

Boor

Wang

et al. 2015

Energy Environ. Sci.

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256

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“…Equation 8 gives the total energy conservation: the first term is for Fourier heat conduction, the second term is the Joule heat per unit volume (W/m 3 ), and the last term is the Peltier heat at a junction or the Thomson heat along the TE material. 17 The Joule heat is always positive, but the Peltier and Thomson heats may be either positive or negative, depending on whether heat is being generated or absorbed.…”

Section: Governing Equations and Model Creationmentioning

confidence: 99%

Three-Dimensional Finite-Element Simulation for a Thermoelectric Generator Module

Takazawa

Nagase

et al. 2015

Journal of Elec Materi

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A three-dimensional closed-circuit numerical model of a thermoelectric generator (TEG) module has been constructed with COMSOL Ò Multiphysics to verify a module test system. The Seebeck, Peltier, and Thomson effects and Joule heating are included in the thermoelectric conversion model. The TEG model is employed to simulate the operation of a 16-leg TEG module based on bismuth telluride with temperature-dependent material properties. The module is mounted on a test platform, and simulated by combining the heat conduction process and thermoelectric conversion process. Simulation results are obtained for the terminal voltage, output power, heat flow, and efficiency as functions of the electric current; the results are compared with measurement data. The Joule and Thomson heats in all the thermoelectric legs, as functions of the electric current, are calculated by finite-element volume integration over the entire legs. The Peltier heat being pumped at the hot side and released at the cold side of the module are also presented in relation to the electric current. The energy balance relations between heat and electricity are verified to support the simulation.

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“…3(b) do not include the error contribution from the specific heat, which is usually between 64% but can show occasionally much higher variations as shown in a previously conducted round robin campaign. 18 …”

Section: Precision and Accuracy Evaluationmentioning

confidence: 99%

Thermal conductivity, electrical resistivity, and dimensionless figure of merit (ZT) determination of thermoelectric materials by impedance spectroscopy up to 250 °C

Beltrán-Pitarch

Prado‐Gonjal

Powell

et al. 2018

Journal of Applied Physics

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Impedance spectroscopy has been shown as a promising method to characterize thermoelectric (TE) materials and devices. In particular, the possibility to determine the thermal conductivity λ, electrical conductivity σ, and the dimensionless figure of merit ZT of a TE element, if the Seebeck coefficient S is known, has been reported, although so far for a high-performance TE material (Bi2Te3) at room temperature. Here, we demonstrate the capability of this approach at temperatures up to 250 °C and for a material with modest TE properties. Moreover, we compare the results obtained with values from commercial equipment and quantify the precision and accuracy of the method. This is achieved by measuring the impedance response of a skutterudite material contacted by Cu contacts. The method shows excellent precision (random errors < 4.5% for all properties) and very good agreement with the results from commercial equipment (<4% for λ, between 4% and 6% for σ, and <8% for ZT), which proves its suitability to accurately characterize bulk TE materials. Especially, the capability to provide λ with good accuracy represents a useful alternative to the laser flash method, which typically exhibits higher errors and requires the measurement of additional properties (density and specific heat), which are not necessarily needed to obtain the ZT.

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Transport Properties of Bulk Thermoelectrics: An International Round-Robin Study, Part II: Thermal Diffusivity, Specific Heat, and Thermal Conductivity

Cited by 140 publications

References 34 publications

Measuring thermoelectric transport properties of materials

Measuring thermoelectric transport properties of materials

Three-Dimensional Finite-Element Simulation for a Thermoelectric Generator Module

Thermal conductivity, electrical resistivity, and dimensionless figure of merit (ZT) determination of thermoelectric materials by impedance spectroscopy up to 250 °C

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