Thermal conductivity measurements of bulk thermoelectric materials

Thermal conductivity is an important material property of the bulk thermoelectrics. To improve ZT a reduced thermal conductivity is always desired. However, there is no standard material for thermoelectrics and the test results, even on the same material, often show significant scatter. The scatter in thermal conductivity made reported ZT values uncertain and sometime unrepeatable. One of the reasons for the uncertainty is due to the microstructure differences resulting from sintering, heat treatment and other processing parameters. We selected commonly used bulk thermoelectric materials and conducted thermal conductivity measurements using the laser flash diffusivity and differential scanning calorimeter (DSC) systems. Thermal conductivity was measured as a function of temperature from room temperature to 500 K and back to room temperature. The effect of thermal cycling on the bulk thermoelectric was studied. Combined with measurements on electrical resistivity and Seebeck coefficient, we show the use of a ZT map in selecting thermoelectrics. The commercial bulk material showed very good consistency and reliability compared to other bulk materials. Our goal is to develop a thermal transport properties database for the bulk thermoelectrics and make the information available to the research community and industry.