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Newswise WASHINGTON, D.C., October 28, 2014 If youve ever gone for a spin in a luxury car and felt your back being warmed or cooled by a seat-based climate control system, then youve likely experienced the benefits of a class of materials called thermoelectrics. Thermoelectric materials convert heat into electricity, and vice versa, and they have many advantages over more traditional heating and cooling systems.

Recently, researchers have observed that the performance of some thermoelectric materials can be improved by combining different solid phases -- more than one material intermixed like the clumps of fat and meat in a slice of salami. The observations offer the tantalizing prospect of significantly boosting thermoelectrics energy efficiency, but scientists still lack the tools to fully understand how the bulk properties arise out of combinations of solid phases.

Now a research team based at the California Institute of Technology (Caltech) has developed a new way to analyze the electrical properties of thermoelectrics that have two or more solid phases. The new technique could help researchers better understand multi-phase thermoelectric properties and offer pointers on how to design new materials to get the best properties.

The team describes their new technique in a paper published in the journal Applied Physics Letters, from AIP Publishing.

An Old Theory Does a 180

Because its sometimes difficult to separately manufacture the pure components that make up multi-phase materials, researchers cant always measure the pure phase properties directly. The Caltech team overcame this challenge by developing a way to calculate the electrical properties of individual phases while only experimenting directly with the composite.

Its like youve made chocolate chip cookies, and you want to know what the chocolate chips and the batter taste like by themselves, but you cant, because every bite you take has both chocolate chips and batter, said Jeff Snyder, a researcher at Caltech who specializes in thermoelectric materials and devices.

To separate the "chips" and "batter" without un-baking the cookie, Snyder and his colleagues turned to a decades old theory, called effective medium theory, and they gave it a new twist.

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"Reverse Engineering" Materials for More Efficient Heating and Cooling