Thermal and Thermoelectric Properties of Nanostructured versus Crystalline SiGe

Nearly 60% of the world´s energy is wasted as heat. Thermoelectric materials can play an important role in green energy harvesting with their ability to convert waste heat into electricity. In this report, thermal and thermoelectric properties of p- type nanostructured silicon germanium (SiGe) as an important high temperature thermoelectric material was studied and compared with those of crystalline SiGe. The materials were synthesized via mechanical alloying and sintering approach. The different synthesis procedures resulted in two different conformation of SiGe. The first one was in nanostructure configuration and the other was in crystalline configuration containing large grains. Thermal and thermoelectric properties of both configurations were investigated in this manuscript. Although, differential thermal analysis (DTA) did not show significant differences between the thermal characteristics of nanostructured and crystalline SiGe, there were major changes in their thermoelectric properties. The nanostructured SiGe had lower electrical conductivity owing to the large scattering rate of electron at the grain boundaries. However, the lower mobility was accompanied by small thermal conductivity in nanostructured SiGe. The Seeback coefficient was grown in nanostructured SiGe as a result of lower carrier concentration. Considering the influence of all these factors, the nanostructured SiGe was thermoelectrically preferred as the figure-of-merit was increased specially at high temperatures.