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

Abstract

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.