Evaluation of monolithic and segmented thermoelectric materials by using a large-temperature-span apparatus

In order to evaluate the thermoelectric properties and power output performance of a gradient TE material under a wide working temperature range, a large-temperature-span apparatus has been developed. However, an accurate evaluation is not so easy to put into practice on the gradient TE material because a lot of difficulties are associated with the heat flow control and the reducing of electrical resistance in the measurement circuit. The present work is a practice to characterize monolithic and segmented thermoelectric materials by the new developed apparatus and approach the method to evaluate a gradient TE material accurately and effectively. This work was carried out for the evaluation of a stacked monolithic (SiGe, PbTe and Bi₂Te ₃) TE leg and a segmented thermoelectric branch (PbTe/Bi₂Te₃), and we confirm their thermoelectromotive force, electrical resistance and temperature distribution both for the apparatus and for specimen stacks. We also made a trial power output evaluation using an electronic load and explore some technical problems in the evaluation of TE materials under a large temperature span. The results of evaluation on power output by electronic load indicate much lower value than the calculation using the real electrical resistance in TE materials. We discuss some problems for the evaluation of stacked thermoelectric materials under a large temperature difference condition