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Direct Evaluation of the Figure of Merit of Thermoelectric Devices by Guarded Hot Plate Method

An apparatus for the evaluation of the figure of merit (ZT) of thermoelectric devices has been developed and ZT values have been estimated for a thermoelectric device. The most challenging problem in ZT value evaluation in this apparatus was measuring the thermal conductivity of the devices precisely. We have solved the problem by introducing a primary thermal conductivity measurement technique, a guarded hot plate method, which makes it possible to obtain directly and simultaneously four physical parameters related to the ZT, namely the thermal conductivity, electrical conductivity, Seebeck coefficient, and absolute temperature. The ZT evaluation was performed by a single scan of the temperature difference between the top and bottom surfaces of the device. We also addressed the thermoelectric properties and the power generation efficiency of a commercial thermoelectric device. The evaluation uncertainty of the ZT value was assessed to secure reliability of the apparatus and was found to be 3.59%.