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, Δ Tmax, is simply related to Z of a thermocouple. However, for thermocouples comprising good thermoelectric materials with [Formula: see text], Δ Tmax 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 Z T and Δ Tmax 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 Δ Tmax 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.