The topic of thermoelectric heats up with promising new magnesium-based materials

Representation of the crystal lattice of the thermoelectric compound Mg3Sb2 (orange magnesium atom, blue antimony). An electric current is generated as heat crosses the material and is propelled by phonon waves. Credits: ORNL / Jill Hemman

The landing of NASA’s Perseverance Rover was another leap not only for space exploration, but also for the technology that powers aircraft in many years of missions on Mars, the thermoelectric generator that converts heat into electricity.

In search of the next leap in thermoelectric technology, researchers at Duke University and Michigan State University have found two magnesium-based materials (Mg).3Sb2 And Mg3Bi2) It can significantly exceed traditional thermoelectric designs, is environmentally friendly and has low manufacturing costs.Contrary to general scientific wisdom regarding the use of Heavy elementResearchers have shown that replacing atoms of heavy elements such as calcium and ytterbium with light magnesium atoms actually improves the performance of magnesium-based materials by a factor of three.

Their study was published in a journal Science AdvancesThe team used neutron and X-ray scattering experiments at the Department of Energy’s Oak Ridge (ORNL) and Argonne National Laboratory, and supercomputer simulations at the National Center for Energy Research and Science (NERSC).Survey in Atomic scale We have elucidated the origin and mechanism behind the ability of materials to convert thermal energy at room temperature into electricity. The findings show the potential for new pathways to improve thermoelectric applications such as Perseverance Rover and myriad other devices and energy generation technologies.

Thermoelectric materials basically generate a voltage from the temperature difference between the hot and cold sides of the material. By converting thermal energy into electricity and vice versa, thermoelectric devices can be used to generate electricity from freezing or thermal exhaust.

“Traditional thermoelectric materials rely on heavy elements such as lead, bismuth, and tellurium, which tend to be expensive because they are neither environmentally friendly nor abundant,” said an associate professor. One Olivier de Rail said. Duke. “On the other hand, magnesium is lighter and more abundant, making it an ideal material for, for example, transportation and space flight applications.”

Delaire usually explained that lighter materials are not very suitable for thermoelectric design because they have too high thermal conductivity. That is, it transfers too much heat to maintain the temperature difference required to generate the voltage. Heavy materials are generally preferred due to their low heat transfer and their ability to store and convert. Thermal energy More efficiently.

“But these magnesium materials have significantly lower thermoelectric conductivity, despite their lower mass densities. These properties open the door to the design of new types of thermoelectric elements that are independent of heavy materials containing toxic elements. It could open, “Delea explained.

The magnesium materials studied by the team belong to a larger class of metal compounds called Zintls. The atomic structure or arrangement of atoms in a gintoru compound makes it relatively easy to experiment and replace various elements in a material. For example, replace heavy elements with light elements for optimal performance and functionality.

“In chemical research, to explore the possibilities of new materials, we need to replace one element with another to see what happens. Usually, we replace it with a chemically similar element in the periodic table. One of the great advantages of using Zintls is that it can be experimented with. There are different elements and different combinations, “said Jins Andin, a graduate student researcher in the Derea group of Duke, the lead author of the paper. Mr. says. “No one expected magnesium to be a better compound, but when a Michigan collaborator replaced magnesium with a component of the material, he was surprised that it was, so he said: The step was to find out why. “

Atoms in a material are neither static nor stationary. They oscillate with increasing amplitude at higher temperatures. Collective vibrations produce a spillover effect called phonons. This looks like a set of waves on the surface of the pond. These waves transport heat through the material. Therefore, measuring the vibration of phonons is important for determining the thermal conductivity of a material.

Neutrons are uncharged and can interact with nuclei, making them very suitable for studying quantum phenomena such as phonons. Delea likened the interaction of neutrons to pulling a guitar string in that it can transfer energy to atoms to excite vibrations and extract hidden information about the atoms in the material.

The team used the Wide Angular-Range Chopper Spectrometer (ARCS) at ORNL’s Spallation Neutron Source (SNS) to measure phonon vibrations. The data they obtained allowed us to trace the preferred low thermal conductivity of the material to a special magnesium bond that interferes with the movement of the phonon wave through the material by interfering with each other.

“Neutrons are one of the best ways to measure atomic vibrations, as we are studying with these materials,” says Ding. “ARCS can detect a wide range of frequencies and wavelengths that help measure the phonon waves contained in a material, which is necessary to better understand how these low thermal conductivity materials work. That’s it. ”

Neutron scattering measurements provided the research team with an extensive study of the internal dynamics of magnesium Zintl materials, helping to guide and improve Ding-led computer simulations and subsequent X-ray experiments. These were used to fully understand the origin of the thermal conductivity of the material.

Using complementary X-ray experiments at Argonne National Laboratory (APS), we zoomed in on certain phonon modes of crystal samples that are too small for neutron measurements. Both neutron and X-ray measurements were consistent with supercomputer simulations performed at NERSC.

In addition to Ding and Delaire, co-authors of this treatise include Tyson Lanigan-Atkins, Mario Calderón-Cueva, Arnab Banerjee, Douglas L. Abernathy, Ayman Said, and Alexandra Zevalkink.

“Thermoelectric is not a bulky engine with moving parts traditionally used to generate electricity from heat, like the Mars rover, but for applications that require a simpler, lighter, and more reliable design. It’s essential, “said Delea. “These magnesium bases material It is a major advance in this area and has the potential to significantly improve power efficiency and open up many possibilities for more advanced thermoelectric applications. ”

“Floppy” atomic dynamics help convert heat into electricity

For more information:
Jingxuan Ding et al, Mg3 (Sb, Bi) 2 thermoelectric element soft anharmonic phonons and ultra-low thermal conductivity, Science Advances (2021). DOI: 10.1126 / sciadv.abg1449

Quote: The topic of thermoelectric is the promising new magnesium-based material acquired from on July 23, 2021 (2021). It gets hot on July 23)

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The topic of thermoelectric heats up with promising new magnesium-based materials

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