The widespread adoption of thermoelectric devices that can directly convert electricity into thermal energy for cooling and heating has been hindered, in part, by the lack of materials that are both inexpensive and highly efficient at room temperature. A new material was developed that works efficiently at room temperature while requiring almost no costly tellurium, a major component of the current state-of-the-art material. Future work could close the slight performance gap between the new material and the traditional material, a bismuth-tellurium-based alloy.
Thermoelectric materials work by exploiting the flow of heat current from a warmer area to a cooler area, and thermoelectric cooling modules operate according to the Peltier effect, which describes the transfer of heat between two electrical junctions. Thermoelectric materials can also be used to turn waste heat — from power plants, automobile tailpipes, and other sources — into electricity and a number of new materials have been reported for that application, which requires materials to perform at far higher temperatures.
Thermoelectric cooling modules have posed a great challenge because they have to work at cooler temperatures, where the thermoelectric figure-of-merit, or ZT, is low because it is dependent on temperature. The figure-of-merit is a metric used to determine how efficiently a thermoelectric material works. Despite the challenge, thermoelectric cooling modules also offer more commercial potential, in part because they can operate for a long lifespan at cooler temperatures; thermoelectric power generation is complicated by issues related to the high temperatures at which it operates, including oxidation and thermal instability.
Bismuth-tellurium alloys have been considered the best-performing material for thermal cooling for decades but the high cost of tellurium has limited widespread use. The new material, comprised of magnesium and bismuth and created in a form carrying a negative charge (known as n-type), was almost as efficient as the traditional bismuth-tellurium material. That, combined with the lower cost, should expand the use of thermoelectric modules for cooling.
To produce a thermoelectric module using the new material, researchers combined it with a positive-charge-carrying, or p-type, version of the traditional bismuth-tellurium alloy. This allowed half as much tellurium to be used.