ABSTRACT
Thermoelectric materials for high temperature applications (T > 700°C/973 K) is still a challenging topic on its own, despite the great success of reaching a high thermoelectric figure of merit zT > 2 at lower temperatures < 427°C for mainly p-type materials. Few high zT n-type materials exist, although e.g., SiGe and (Hf,Zr)(Ni,Sn) half-Heusler alloys with zT ~1 @ ~627°C are among the more promising ones. For a sustainable energy society, it is important to recycle the waste heat at high temperatures in some way, either by production of steam to drive a turbine or converting it to electricity directly by using the temperature gradient that is formed naturally between the heat source and the outer environment. The latter option is very attractive and would require a thermoelectric device that can directly convert heat into useful electricity. This chapter discusses the basic principles behind thermoelectric materials, some common materials, and the overall properties that it is necessary to control to achieve efficient thermoelectric materials. In addition, the chapter focus on approaches to find new materials with a high zT and materials with high power factors over a broad temperature range, such as the recently reported high entropy alloys.
