Defects Can “Hulk-Up” Materials
Lawrence Berkeley Labs, May 20, 2015. Image credit: LoggaWiggler
In the story of the Marvel Universe superhero known as the Hulk, exposure to gamma radiation transforms scientist Bruce Banner into a far more powerful version of himself. In a study at Berkeley Lab, exposure to alpha-particle radiation has been shown to transform certain thermoelectric materials into far more powerful versions of themselves.
“We’ve demonstrated that by irradiating a thermoelectric semiconductor with high-energy alpha particles, we can control native defects in the crystal so that these defects actually enhance the performance of the thermoelectric material by a factor of up to ten,” says Junqiao Wu, a physicist who holds joint appointments with Berkeley Lab’s Materials Sciences Division and the University of California Berkeley’s Department of Materials Science and Engineering. “Although this discovery goes against common wisdom, it turns out that when properly managed, a damaged thermoelectric material is a better thermoelectric material.”
The ability of thermoelectric materials to convert heat into electricity, or electricity into cooling, represents a potentially huge source of clean, green energy. Consequently, thermoelectric materials have been heavily investigated over the past several decades. Past studies have shown that the efficiency of heat-to-electricity conversion – a metric known as the “figure-of-merit” or ZT – is inherently limited by the coupling of three key parameters: electrical conductivity, thermopower and thermal conductivity.
“Usually thermopower is enhanced at the cost of a reduction in electrical conductivity,” Wu says, “but we have been able to break this undesired coupling and demonstrate simultaneous increases in electrical conductivity of up to 200-percent, and thermopower of up to 70-percent.”