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# Wiggling of Silver Atoms Offers Key to Thermoelectricity

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X-ray evaluation reveals lattice distortions are behind silver gallium telluride’s thermoelectric properties, a discovering that might advance inexperienced applied sciences.

Supplies that convert warmth into electrical energy or electrical energy into warmth are predicted to be environment friendly power harvesters, giving them the potential to rework inexperienced applied sciences. Whereas these “thermoelectric” supplies have made their technique to Mars, the place they assist energy rovers, they’re not often used on Earth, partially due to a shortage of supplies with the correct mix of properties—excessive electrical conductivity coupled with low thermal conductivity. Now, Mercouri Kanatzidis of Northwestern College, Illinois, and colleagues have recognized a brand new materials with these properties [1]. The crew believes that the discovering may assist researchers discover different thermoelectric supplies.

Kanatzidis and postdoctoral scholar Hongyao Xie have been learning the thermal properties of the semiconducting materials silver gallium telluride (

${\text{AgGaTe}}_{2}$

), once they observed one thing uncommon about its habits. As an alternative of exhibiting excessive thermal conductivity, like its copper-based counterpart, the fabric appeared to have an especially low conductivity that contradicted predictions.

To grasp the reason for this discrepancy, the duo determined to take a more in-depth look and examine the fabric’s atomic crystal symmetry. They teamed up with researchers at Brookhaven Nationwide Laboratory (BNL), New York, and utilized that facility’s synchrotron gentle supply to review supplies on the nanoscale. Observing the lattice construction of their

${\text{AgGaTe}}_{2}$

samples, the crew discovered that its anticipated diamondoid lattice—one the place the association of the atoms has the identical spatial sample as these in a diamond crystal—was distorted. The silver atoms didn’t sit the place they have been imagined to.

In

${\text{AgGaTe}}_{2}$

, silver atoms are anticipated to take a seat on the middle of a tellurium tetrahedron, creating the diamondoid lattice construction. However the x-ray evaluation revealed as a substitute that the silver atoms’ positions have been off middle and that their precise areas fluctuated over time. Because the crew heated the fabric, they discovered that these fluctuations elevated in magnitude, disrupting the lattice construction’s international symmetry. From the experimental information and from computational modeling, the crew decided that this temperature-induced lattice distortion—a uncommon phenomenon referred to as emphanisis—was the foundation reason behind the fabric’s low thermal conductivity, says Emil Bozin of BNL, who led the structural evaluation a part of the venture.

“For a while, different researchers within the semiconductor group have been impressed to find out the potential of diamondoid compounds as thermoelectric supplies,” Kanatzidis says. “We suspected that there was extra science right here than met the attention.”

The work is a “lovely” deep dive into an space of analysis that might have broad ranging implications, says Zhiting Tian, a mechanical and aerospace engineer at Cornell College whose analysis focuses on thermal switch, conversion, and storage. “Ultralow thermal conductivity is all the time favorable for thermoelectric purposes, because it helps to take care of the temperature gradients between the cold and warm sides [of a device] and cut back warmth loss,” she provides. “This work presents new insights into engineering diamond-type constructions that possess ultralow thermal conductivity.”

The crew now plans to research whether or not including silver to different supplies can induce in them comparable temperature-dependent lattice deformations and thermoelectric behaviors. The following step of this analysis is to make use of this discovering to see the way it impacts the thermoelectric efficiency of different diamondoid compounds, Xie says. Past thermoelectricity, the crew additionally thinks that the heat-dependent habits of

${\text{AgGaTe}}_{2}$

may doubtlessly influence each how shortly electrons can transfer by means of the fabric below completely different circumstances and the way the fabric emits electrons when illuminated with gentle, properties vital to be used of the fabric in photo voltaic cells and different optics purposes.

–Sarah Wells

Sarah Wells is an unbiased science journalist based mostly in Boston.

## References

1. H. Xie et al., “Hidden native symmetry breaking in silver diamondoid compounds is root reason behind ultralow thermal conductivity,” Adv. Mater. 2202255 (2022).

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