Evaluation of the Figure of Merit on Thermoelectric Materials by Harman Method

The figure of merit ZT of thermoelectric materials has been evaluated by the Harman method in the temperature region below room temperature. In this method only resistance measurements by both dc and ac methods are required to obtain the ZT values. ZT is given by ZT =( R dc / R ac -1)/ x , where R dc , R ac and x are the resistance value by the ac and dc methods and the rate of the heat to the heat bath, respectively. The heat effect is experimentally confirmed to be negligibly small and we can use x =1 which corresponds to a sufficient adiabatic condition. Because an ambiguity due to experimental errors such as the length between the measurement terminals in the resistivity and the thermal conductivity measurements is removed, ZT can be determined very simply and precisely by the Harman method.