Determination of ZT of PN thermoelectric couples by AC electrical measurement

In this work we use the thermoelectric coupling between Peltier and Seebeck effects to determine the ZT of a bismuth telluride thermoelectric couple. This coupling acts as thermal induction and produces a voltage drop induced by the Peltier thermal gradient in addition to the resistive voltage. In sine wave current excitation, the relative contribution of these two terms depends on electrical and thermal properties of materials as well as the current frequency. The use of a lock-in amplifier allows to separate the Peltier contribution at the current frequency from the Joule one at twice the current frequency. We have developed two original models to simulate the electro-thermal behavior of the thermoelectric couple. The first one is based on thermal quadrupole and allows an analytical resolution. The second one uses an electrical simulator as SPICE. In order to control ambient temperature and boundary conditions, we have designed a specific sample holder for such kind of measurement. An optimization procedure allows the identification of electrical and thermal conductivity and thermoelectric power. From this we can determine with a good accuracy the ZT of the couple by a simple electrical measurement, this method is suitable for many kinds of samples.