In 1821 Thomas Seebeck measured a magnetic flux through the plane of a circuit made by joining dissimilar wires and holding the two junctions at different temperatures. Although Seebeck did not recognize it at the time, we now attribute the effect to the migration of electrical charges (electrons or holes) away from the heat source. Materials exhibiting that thermoelectric effect can be characterized by the Seebeck coefficient S, the ratio of the potential drop to the temperature gradient applied.
As sketched in figure 1, one can exploit the effect to generate electrical energy from a thermal gradient—or, when run backward, to transfer heat by application of an electrical potential. In the mid 1950s, a brief flurry of research activity was aimed at producing refrigerators with no moving parts. The research on thermoelectrics has accelerated again over the past few decades,1 driven by a push toward greater energy...
