Lead Tellurides alloyed with Germanium and Silicium - Thermal Conductivity

In the lead telluride materials PbTe-Ge and PbTe-Ge1-xSix the Thermal ConductivityThermal conductivity (λ with the unit W/(m•K)) describes the transport of energy – in the form of heat – through a body of mass as the result of a temperature gradient (see fig. 1). According to the second law of thermodynamics, heat always flows in the direction of the lower temperature.thermal conductivity is easily tuned by alloying Ge with Si and reducing the Ge content [2] .

The below shown results are obtained in the temperature range between 25°C and 320°C. Plot A shows that Ge has a significant influence in the lattice conductivity of PbTe. With decreasing Ge content the lattice conductivity decreases over the entire temperature range. In addition, alloying Ge with Si of the PbTe-Ge (20%) composition a further reduction of the lattice conductivity can be observed (plot B). Similar behavior can be seen at constant mixing ratio of Ge and Si and decreasing Ge0.8Si0.2 content (plot C). Plot D shows that a ratio of 5% Ge-/Ge-Si achieves an optimum lattice thermal conductivity.  
[2] Sootsman, Joseph R.; He, Jiaqing; Dravid, Vinayak P., Li, Chang-Peng; Uher, Ctirad; Kanatzidis, Mercouri G. High Thermoelectric Figure of Merit and Improved
Mechanical Properties in Melt Quenched PbTe – Ge and PbTe – Ge1-xSix Eutectic and Hyper-eutectic Composites J. Appl. Phys. (2009), 105, 083718. (measurement with LFA 457 MicroFlash®®)