Hendrik Kolb

Simultaneous measurement of all thermoelectric properties of bulk materials in the temperature range 300–600 K

Thermoelectric materials can directly convert heat into electrical energy. The characterization of different materials is an important part in thermoelectric materials research to improve their properties. Usually, different methods and setups are combined for the temperature dependent determination of all thermoelectric key quantities - Seebeck coefficient, electrical conductivity, and thermal conductivity. Here, we present a measurement system for the simultaneous determination of all of these quantities plus the direct determination of the figure of merit by means of the Harman method (zT)H in a temperature range from room temperature up to 600 K. A simultaneous measurement saves time and reduces the measurement error, and the change of all material properties can be monitored even for unstable materials. Thermal conductivity measurements are inherently affected by undesired thermal losses, in particular, through radiation at higher temperatures. We show a simple experimental approach to measure radiation losses and correct for those. Comparative measurements on traditional systems show good agreement for all measured quantities.

Thermoelectric transport and microstructure of optimized Mg2Si0.8Sn0.2

Solid solutions of magnesium silicide and magnesium stannide exhibit excellent thermoelectric properties due to favorable electronic band structures and reduced thermal conductivity compared to the binary compounds. We have optimized the composition Mg2Si0.8Sn0.2 by Sb doping and obtained a thermoelectric figure of merit close to unity. The material comprises of several phases and exhibits intrinsic nanostructuring. Nevertheless, the main features of electronic transport can be understood within the framework of a single parabolic band model. Compared to Mg2Si we observe a comparable power factor, a drastically reduced thermal conductivity and an increased effective mass.