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_TE, 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_lead/K_TE, which represents the relationship between the thermal conductance of the thermoelectric material K_TE and that of the lead wires causing heat leakage K_lead, was also evaluated. The effective dimensionless figure of merit zT_eff was estimated at various K_lead/K_TE 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_TE = 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_lead/K_TE > 0.1 is required when performing K_lead/K_TE-dependent experiments on the modules with zT = 0.8645.