Visualizing Thermal and Electrical Contacts in ThermoelectricLegs by Microscopic Lock-In Thermography

Establishing stable contact between thermoelectric (TE) materials, electrodes, and antidiffusion materials is crucial for enabling practical applications of high-performance TE materials in power generators under harsh operating conditions. These contacts were analyzed in this study by microscopic lock-in thermography. Electrical failures near the contacts were visualized based on their Joule heating characteristics, with background noises corresponding to Peltier heating and Joule heating from the TE material being nullified by a high-amplitude AC current and the lock-in principle, respectively. Additionally, failures related to thermal contact were visualized based on the attenuation factor of the temperature oscilation under periodic heating, thereby enabling independent electrical and thermal evaluations of the contacts. The effectiveness of the established method was demonstrated by examining state-of-the-art TE materials such as nanostructured PbTe, FeNbSb, Ca_2.7Bi_0.3Co₄O₉, and Cu₂₆Ti₂Sb₄Ge₂S₃₂-based material.