Applicability limits of time-domain impedance spectroscopy for comprehensive thermoelectric characterization under heat leakage conditions

We measured the complete set of thermoelectric parameters using the time-domain impedance spectroscopy (TDIS) method with controlled heat leakage on a bismuth-telluride-based Π-shaped thermoelectric module over the temperature range of 100-300 K. The resistivity and dimensionless figure of merit (zT) were determined to be 2.341 µΩ m and 0.111 ± 0.001 at 100 K, and 10.194 µΩ m and 0.8645 ± 0.0003 at 300 K, respectively. The corresponding thermal conductivities were 2.443 ± 0.396 W/m K at 100 K and 1.259 ± 0.003 W/m K at 300 K. Based on the definition of zT, the absolute values of the Seebeck coefficient were calculated as 79.74 ± 8.72 µV/K at 100 K and 192.32 ± 0.93 µV/K at 300 K as effective values. These results confirm that the TDIS method enables complete thermoelectric characterization using electrometric measurements. We further analyzed the conditions required to achieve high measurement accuracy within specified error margins. Our findings indicate that the critical factors are the relative error in zT during measurements and the thermal conductance ratio between the thermoelectric element and the lead wires responsible for heat leakage.