Liquid-like material could yield better thermoelectric devices

Made up of copper and selenium, the novel material is physically a solid, but exhibits liquid-like behaviors due to the way its copper atoms flow through the selenium's crystal lattice. "It's like a wet sponge," explained Jeff Snyder, a faculty associate in applied physics and materials science at the California Institute of Technology. "If you have a sponge with very fine pores in it, it looks and acts like a solid. But inside, the water molecules are diffusing just as fast as they would if they were a regular liquid. That's how I imagine this material works. It has a solid framework of selenium atoms, but the copper atoms are diffusing around as fast as they would in a liquid." According to Synder, the material was first used by NASA engineers 40 years ago, but its liquid-like properties were not properly understood. What the researchers have since discovered is that unlike most thermoelectric materials, the copper-selenium compound is good at conducting electricity and bad at conducting heat. The team found that the crystal structure of the selenium helps conduct electricity, while the free-flowing copper atoms behave like a liquid, damping down thermal conductivity. According to the scientists, the material's figure of merit (a rating for thermoelectric efficiency) is one of the highest ever recorded for a bulk material. "Hopefully, the scientific community now has another strategy to work with when looking for materials with a high thermoelectric figure of merit," Snyder concluded.