Scientists, at the Vienna University of Technology have developed a new class of thermoelectric materials they claim can be used to create electricity more efficiently.
According to the researchers, the material’s unique structure, which consists of countless tiny magnetic crystal “cages” known as clathrates with cerium atoms enclosed inside, is the key reason for its increase in efficiency. The trapped atoms are constantly rattling the “bars” of their cages, say the researchers, creating some of the materials’ special properties.
“These clathrates show remarkable thermal properties,” Professor Silke Bühler-Paschen of Vienna University of Technology said. Since the exact behavior of the material depends on the interaction between the enclosed atoms and the cage surrounding them, “we came up with the idea to trap cerium atoms, because their magnetic properties promised particularly interesting kinds of interaction,” he explained.
Using a crystal growth technique in a mirror oven, Professor Andrey Prokofiev of Vienna University of Technology was able to create clathrates made of barium, silicon and gold, encapsulating single cerium atoms. Experiments performed by the research team showed that the cerium atoms increased the material’s thermoelectric power by 50 percent, allowing for a much higher voltage to be obtained.
“The reason for these remarkably good material properties seem to lie in a special kind of electron-electron correlation – the so-called Kondo effect,” Bühler-Paschen said. The Kondo effect describes the scattering of conduction electrons in a metal due to magnetic impurities, resulting in a characteristic change in electrical resistivity with a change in temperature.
“The rattling of the trapped cerium atoms becomes stronger as the temperature increases. This rattling stabilizes the Kondo effect at high temperatures. We are observing the world’s hottest Kondo effect,” Bühler-Paschen explained.
The research team plans to replicate the effect with other kinds of clathrates and investigate whether other metals can be used as a substitute for gold in order to make the material more attractive commercially.