Hidden distortions trigger promising thermoelectric property

Study describes new mechanism for lowering thermal conductivity to aid search for materials that convert heat to electricity or electricity to heat

In a world of materials that normally expand upon heating, one that shrinks along one 3D axis while expanding along another stands out. That’s especially true when the unusual shrinkage is linked to a property important for thermoelectric devices, which convert heat to electricity or electricity to heat.

In a paper just published in the journal Advanced Materials, a team of scientists from Northwestern University and the U.S. Department of Energy’s Brookhaven National Laboratory describe the previously hidden sub-nanoscale origins of both the unusual shrinkage and the exceptional thermoelectric properties in this material, silver gallium telluride (AgGaTe2). The discovery reveals a quantum mechanical twist on what drives the emergence of these properties—and opens up a completely new direction for searching for new high-performance thermoelectrics.

“Thermoelectric materials will be transformational in green and sustainable energy technologies for heat energy harvesting and cooling—but only if their performance can be improved,” said Hongyao Xie, a postdoctoral researcher at Northwestern and first author on the paper. “We want to find the underlying design principles that will allow us to optimize the performance of these materials,” Xie said.

Thermoelectric devices are currently used in limited, niche applications, including NASA’s Mars rover, where heat released by the radioactive decay of plutonium is converted into electricity. Future applications might include materials controlled by voltage to achieve very stable temperatures critical for operation of high-tech optical detectors and lasers.

The main barrier to wider adoption is the need for materials with just the right cocktail of properties, including good electrical conductivity but resistance to the flow of heat.

Read more on the BNL website

Image: Brookhaven Lab members of the research team: Simon Billinge, Milinda Abeykoon, and Emil Bozin adjust instruments for data collection at the Pair Distribution Function beamline of the National Synchrotron Light Source II. In this setup, a stream of hot air heats samples with degree-by-degree precision as x-rays collect data on how the material changes.