Material boosts thermoelectricity

Scientists have been searching for decades for more efficient ways to convert heat to electricity. Thermoelectric materials generate electricity when heated and turn cold in the presence of electrical current.

The measure of success for converting materials is the ZT factor, a formula that includes thermal power, electrical conductivity, thermal conductivity and temperature. A ZT factor over three would make thermoelectric power generation competitive with home refrigerators and power generators. Forty years ago the best ZT factor in existence was 0.6. After four decades of research, it stood at one.

Researchers from Michigan State University, the University of Michigan at Ann Arbor, and Aristotle University of Thessaloniki in Greece have discovered a new family of thermoelectric semiconductor materials that raises the bar considerably. The researchers' material has a ZT factor of 2.2 at 527 degrees Celsius, which may be high enough for practical electricity generation.

The high temperature rules out refrigeration applications, however.

The researchers' material is a mix of silver, lead, antimony and tellurium. One of the keys to its utility is very tiny areas, or nano dots, where the crystal structure of the material is rich in silver and antimony and surrounded by a silver-antimony-poor region.

There is evidence that the material could be further improved, according to the researchers. The work appeared in the February 5, 2004 issue of Science.