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Thermoelectric reference materials for Seebeck coefficients


Figure. 1: Heating sleeve for the temperature-dependent measurement of Seebeck coefficients

Thermoelectric materials convert thermal energy directly into electric energy, and vice versa. The effectiveness of the energy conversion depends on the transport properties of the materials, on the Seebeck coefficient S, on the electric conductivity σ and on the thermal conductivity κ, which are summarized in the thermoelectric figure of merit ZT = S2σT/κ (T: absolute temperature). The exact determination of ZT is the pre-condition required to assess and compare newly developed thermoelectric materials. To this end, measurements of the transport properties that are traceable to the SI units are indispensable. With the aid of a measuring system which is installed at PTB, the Seebeck coefficients and the electric conductivities of thermoelectric bulk materials and of thin layers can be measured with low uncertainties.

The Seebeck coefficient is a temperature-dependent material parameter which describes the voltage drop caused by a temperature gradient over a sample and which decisively determines the ZT value of thermoelectric materials. Within the scope of the EMRP project "Metrology for Energy Harvesting", reference materials have been metrologically investigated and characterized for the first time, at PTB and worldwide, with regard to their Seebeck coefficients in the higher temperature range between 300 K and 850 K. This temperature range is important for applications, e.g., in the automotive area. The measurement uncertainties attained for the Seebeck coefficients of the two reference materials ISOTAN® and bismuth-doped lead telluride lie between 2.5 % and 8 %, depending on the material and on the temperature. Both certified materials can be obtained from PTB.

Opens external link in new windowE. Lenz, F. Edler, P. Ziolkowski: Int. J. Thermophys. 34, 1975 (2013)


F. Edler, 7.41, e-mail: Opens window for sending emailFrank.Edler(at)ptb.de