Measurements of thermoelectric figure of merit based on multi-harmonic thermal analysis of thermographic images

We demonstrate a versatile measurement method for the thermoelectric figure of merit and related transport properties by means of a multi-harmonic thermal analysis of a thermographic movie. The method is based on the thermal analyses of the charge-current-induced temperature distribution generated by the Peltier effect at the first harmonic and by Joule heating at the second harmonic, measured with an infrared camera. This allows simultaneous estimation of the thermal diffusivity, thermal conductivity, volumetric heat capacity, and Peltier/Seebeck coefficient of conductors without attaching an external heater. The thermal analysis developed here is applicable to a system with the interfacial thermal resistance between the target conductor and reference material. Our method enables the measurements while applying an external magnetic field, opening the way for investigating the magnetic field and/or magnetization dependences of the figures of merit and associated properties for the magneto-thermoelectric effects. We demonstrate the usability of this method by estimating the figures of merit for the Peltier/Seebeck, magneto-Peltier/Seebeck, and Ettingshausen/Nernst effects in a Bi–Sb alloy as a promising material for thermoelectric applications. The multi-harmonic thermal analysis method will, thus, aid in developing highly efficient thermoelectric materials and further investigations of magneto-thermal and magneto-thermoelectric transport properties.