Thermoelectric Properties and Thermal Stability of Nanostructured Thermoelectric Materials on the Basis of PbTe, GeTe, and SiGe

Abstract

We have developed compositions and methods for obtaining effective medium-temperature nanostructured thermoelectric materials (TEMs): PbTe (doped by 0.2 wt % PbI2, 0.3 wt % Ni), GeTe (doped by 7.4 wt % Bi), high-temperature Si0.8Ge0.2 (doped by 1.7 wt % P) and Si0.8Ge0.2 (doped by 0.5 wt % B). Using scanning electron microscopy, the composition and structure of the materials are studied. The temperature dependence of the electrical conductivity and thermoelectric power of TEMs are explored. The thermal conductivity of TEMs are studied by the absolute stationary method. The components of thermal conductivity are determined. A decrease in thermal conductivity in nanostructured materials by 10–15% in comparison with the usual structure due to phonon heat transfer has been found. The obtained data are used to calculate the thermoelectric figure of merit (Z) and parameter ZТ. For nanostructured TEMs based on PbTe, GeTe, and n-type Si0.8Ge0.2, the temperature dependences of specific heat have been studied for the first time using differential scanning calorimetry (DSC). With the help of repeated DSC measurements, it has been found that nanostructured TEMs are thermally stable in the working temperature ranges. Thermogravimetric analysis is carried out and temperatures are determined at which a significant TEM sublimation occurs. The ranges of operating temperatures at which the investigated TEMs have the maximum efficiency and thermal stability have been determined. This is urgent in modeling multisectional thermoelements operating in a wide temperature range.