Direct Comparison of Thermoelectric Devices Using Impedance Spectroscopy

The thermoelectric properties of devices based on bismuth telluride, skutterudite, and calcium manganese oxide have been investigated and compared using impedance spectroscopy at 23 degrees C. Prior to the detailed analysis, Kramers-Kronig transformation tests were performed to examine the validity of the obtained impedance spectra. All the spectra were Kramers-Kronig transformable, and were interpreted using equivalent circuit fitting. The three key parameters (Seebeck coefficient, thermal conductivity, and electrical conductivity) and dimensionless figure of merit of bismuth telluride and skutterudite-based devices were successfully extracted from their respective impedance spectra. However, the thermal conductivity of the calcium manganese oxide-based device was overestimated, while the Seebeck coefficient and electrical conductivity values were reasonably accurate owing to their negligible thermoelectric effect at 23 degrees C. We further proposed that the thermoelectric capacitance obtained from the impedance spectra could be a quantitative measure of the propensity of thermoelectric devices to generate thermoelectric power under an external temperature gradient.