Easy-to-make doped thermoelectric materials

Thermoelectric materials, which can convert electric voltage into various temperature differences, ranging from hot to cold, and vice-versa, have been used in refrigerators for over 20 years, but these applications are still small and highly inefficient. This is due to the fact that these materials are costly and expensive to produce in large amounts, while their combinations of thermal and electrical properties are not necessarily optimal.
Engineering researchers at Rensselaer Polytechnic Institute, Troy, NY, USA, developed a new method for creating enhanced nano-structured thermoelectric materials, doped thanks to the presence of infinitesimal amounts of sulphur. One outstanding feature of the doped material is that it is obtained by cooking the material and the dopant (the sulphur) together in a standard microwave oven. The obtained material exhibits better physical properties than those of other thermophysical materials currently available on the market.
The difficulty in engineering thermoelectric materials is due to the need to control separately the electric conductivity, the thermal conductivity and the Seebeck coefficient (which measures the magnitude of an induced thermoelectric voltage in response to a temperature difference across the material). As these properties are interrelated, manipulating one necessarily affects the other two, but the Rensselaer team worked at finding a new way to minimize the interdependence of these properties, by combining doping and nanostructuring in well-known thermoelectric materials such as tellurides and selenides based on bismuth and antimony.
The aim is to create thermoelectric material with a high “figure of merit” or ZT (i.e. a measure of how efficient the material is at converting heat to electricity). This material demonstrated a ZT of 1-1.1 at room temperature. Its makers claim that “such high figures” were obtained “even without optimizing the process”, leaving plenty of scope for obtaining higher ZT with some smart engineering. Furthermore, Rensselaer claim the technology could pave the way to the making of high-efficiency cooling devices, systems to cool computer chips, or solid-state thermoelectric devices for harvesting waste heat or solar heat and converting it into electricity.
Rensselaer Polytechnic Institute, Troy, NY February 3, 2012