Commercialized bulk constantan with a low dimensionless figure of merit and its film fabricated by electroplating were prepared to demonstrate the feasibility of impedance spectroscopy for estimating thermoelectric parameters. From the frequency dependence of the impedance, the resistivity and dimensionless figure of merit were directly estimated as 5.3 × 10−7 Ωm and 0.026 for the bulk and 3.8 × 10−7 Ωm and 0.0098 for the film at room temperature (302 K), respectively. We concluded that impedance spectroscopy is a suitable technique for estimating the thermoelectric parameters of any material with an apparent Seebeck coefficient.
This study has investigated variations in the carrier scattering mechanisms of polycrystalline bismuth based on the temperature dependence of its transport coefficients across a range of temperatures from 10 to 300 K. A measurement of the continuous temperature dependence of the Hall coefficient revealed the characteristic extremes of its temperature-based parameters to be less than 50 K. The results demonstrated a clear variation in the component of the scattering mechanism pertaining to acoustic deformation. Furthermore, the temperature dependencies of carrier density, mobility, chemical potential, and band gap energy were also comprehensively investigated to determine their influence on carrier transport. The information obtained in this study is quite relevant for the realization of the carrier transport of Bi nanowire. The carrier transport of the wire exhibits a mean free path that is equivalent to the wire diameter and has been expected to introduce a quantum effect, thus enhancing the thermoelectric performance.
The influence of contact resistance between a polycrystalline bismuth as a basic thermoelectric material and electrodes made of copper using binders of Ag epoxy and conventional solder was investigated to estimate the dimensionless figure of merit (zT) via impedance spectroscopy (IS). The frequency dependence of the impedance using both binders was measured at 300 K under an appropriate alternating current because a considerably larger Peltier heat was required, relative to Joule heat, for estimating the zT precisely. Through the duo-IS method, zT at 300 K was estimated to be 0.126 ± 0.004 and 0.130 ± 0.002 using the Ag epoxy and solder, respectively. The temperature dependence of zT from 300 to 30 K was also estimated, and zT > 0.01 was a practical based on this technique, owing to its signal–noise ratio. The duo-IS method is invaluable for estimating zT in the entire temperature region based on an appropriate configuration.
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