The challenge in any effort to discover new thermoelectric (TE) materials lies in achieving simultaneously high electronic conductivity, high thermoelectric power and low thermal conductivity in the same solid. These properties define the thermoelectric figure of merit ZT = (S²s/k )T; where S is the thermopower, s the electronic conductivity, k the thermal conductivity, and T the temperature. The first three quantities are determined by the details of the electronic structure and scattering of charge carriers (electrons or holes) and thus are not independently controllable parameters. The thermal conductivity has a contribution from lattice vibrations, k_l, which is called the lattice thermal conductivity. Thus k = k_e + k_l, where k_e is the carrier thermal conductivity.

Efforts aim to synthesize bulk materials with higher figures of merit than those attainable with Bi₂Te₃. Several new ideas and approaches to the design of improved thermoelectric materials have stimulated a resurgence of interest in this old field. The least understood problem is how to increase the thermopower of a material without depressing the electronic conductivity and how to predict precisely which materials will have very large thermopower.

There are many different approaches and avenues taken by different groups around the world.  The approach to new thermoelectric materials is to explore the complex chalcogenide materials by using newly developed solid state synthetic techniques for these systems.

There is not merely interested in new compounds that are substitutions and variations of known structures, but in entirely new structure types. If significantly enhanced TE properties are to be found, new materials must become available. Therefore, novel types of syntheses must be explored to allow for higher ZTs. Since the electrical properties of solids are directly dependent on their crystal structure, the motivation to look for new materials with new lattice structures.

Interest in TE materials is not new but the need for new materials is increasing and the next decade will be critical in the development of this field. Taking into account the difficulty in identifying the "right" compound and optimizing to ZT > 1, long term sustainable planning is necessary and close collaboration between chemists, physicists and engineers is key to success. Such collaborative approaches have been the paradigm in which the present effort is based.  Michigan State University is currently developing a 1kW thermoelectric generator.  This effort is being supported by The Office of Naval Research.

1kW Thermoelectric Generator Setup