Measuring thermoelectric module properties by time-domain impedance spectroscopy using heat leakage at 300 K.

All key thermoelectric properties of thermoelectric materials (i.e., resistivity ρ, dimensionless figure of merit zT, thermal conductivity κ, and Seebeck coefficient S) were measured at 300 K using time-domain impedance spectroscopy (TDIS). This method accounted for heat leakage through lead wires connected to a bismuth-telluride-based Π-shaped thermoelectric module. The values of ρ and zT, without considering heat leakage, were rapidly determined in the frequency domain using impedance measurements with alternating current and in the time domain through transient-response measurements with direct current. The thermal conductance ratio K/K, which represents the relationship between the thermal conductance of the thermoelectric material K and that of the lead wires causing heat leakage K, was also evaluated. The effective dimensionless figure of merit zT was estimated at various K/K ratios to assess the influence of heat leakage. At 300 K, the estimated thermoelectric parameters were ρ = 10.19 μΩm, zT = 0.8645 ± 0.0003, κ = 1.259 ± 0.003 W/mK, and |S| = 192.3 ± 0.4 μV/K. The results indicate that for accurate determination of all thermoelectric parameters using TDIS, the condition K/K > 0.1 is required when performing K/K-dependent experiments on the modules with zT = 0.8645.