Thermoelectric figure-of-merit from Peltier cooling

Abstract

We use Peltier cooling to experimentally determine the thermoelectric figure-of-merit of a material, where the maximum temperature depression, ΔTmax, is simply related to Z of a thermocouple. However, for thermocouples comprising good thermoelectric materials with ZT≥1, ΔTmax can be large (≥100 K), making it difficult to assign the measurement to a particular temperature. This is less of a problem if the thermocouple consists of a semiconductor and a metal since ZT and ΔTmax are then much smaller. We developed a procedure for measuring the dimensionless figure-of-merit of a semiconductor using semiconductor-metal thermocouples in which the form factor (i.e., the ratio of areas to lengths of the two branches) is optimized. We also show valuable aspects in the ΔTmax measurement when the material dimensions are varied. Our experiments on couples consisting of a bismuth telluride alloy and constantan, and the corresponding theoretical analysis, show that the radiation losses are significant at ordinary temperatures. A good estimate of thermal conductivity and zT of the sample can be obtained when radiation losses are minimized.