Experimental and Modeling Study of Thermoelectric Materials for High Figure of Merit

Half-Heusler alloys RNiSn (R=Hf, Zr, Ti) were made by arc melting under argon atmosphere followed by the consolidation using Spark Plasma Sintering (SPS) technique. The thermoelectric properties were measured from room temperature up to 1170 K. The temperature dependences of thermoelectric properties and structures were investigated. A frequency-dependent differential effective medium (DEM) model was developed to evaluate the lattice thermal conductivity. This model was also applied to calculate the thermal conductivity of nanostructured Si and Si80Ge20 systems. The calculation results were compared with the experimental data measured with time-domain thermoreflectance to investigate length scale effects on phonon wavelength, mean free path, as well as the resulting impact on the thermal conductivity.