In Situ Thermoelectric Property Characterization of Microscale Single Thermoelectric Fiber Based on Harmonic Detection

Exploring advanced thermoelectric materials, especially flexible thermoelectric fibers, is promising for wearable devices. The thermoelectric properties of these fibers are evaluated using the figure of merit ZT value. However, there is a lack of empirical research on the properties of microscale thermoelectric fibers, necessitating the development of precise measurement methods. In addition, since the properties of micro- and nanofiber materials can be affected by the microstructure, separate measurements of electrical conductivity, Seebeck coefficient, and thermal conductivity before calculating the ZT values can lead to large errors in the final calculations. In this study, Bi₂Te_2.7Se_0.3 thermoelectric fibers are prepared and measured by using a thermally drawn method and an in situ method, respectively. The in situ measurements are carried out using a self-developed instrument capable of measuring temperatures from room temperature up to 1,200 K, suitable for sample sizes ranging from micro- to nanoscale. The uncertainty of the measurement exhibits less than 6.36%. The results indicate that the thermal drawing process influences crystal growth, enhancing the Seebeck coefficient and reducing electrical conductivity and thermal conductivity. Moreover, the accuracy of the measurement method is verified by pure Pt wire. The integrated in situ measurement effectively reduces experimental errors due to sample differences when calculating parameters for multiple samples measured individually, and the maximum error that can be reduced is 19.5%. This research contributes a practical measurement method of thermoelectric fibers and advances the development of wearable thermoelectric devices.