Researchers harness the power of a new solid-state thermal technology
tech innovation 2022
By Karen Walker, University of Virginia School of Engineering and Applied Science
Nature Communications (2022). DOI: 10.1038/s41467-022-29023-Y” width=”800″ height=”525″/> Structural phase change in PZO upon electrical and thermal stimuli. a) Reciprocal space map of PbZrO3 440/280O and DyScO3 332O reflections showing epitaxial growth and the presence of ferroelastic domains in the epitaxial film. b) Polarization–electric field hysteresis response for epitaxial PbZrO3 film showing antiferroelectric switching. c) 2θ–ω XRD pattern for polycrystalline PbZrO3 film. d) Channeling-contrast backscatter electron micrograph of the polycrystalline PbZrO3 film. Arrows indicate the locations of clearly resolved ferroelastic domains. e) Phase diagram for lead zirconate titanate (PbZr1−xTixO3, PZT) constructed from ref. 27. f) Schematic of the dipole orientation in the antiferroelectric to ferroelectric (AFE-to-FE) and antiferroelectric to paraelectric (AFE-to-PE) phase transitions. credit: Kiumar Aryana et al, nature communication (2022). DOI: 10.1038/s41467-022-29023-Y
Structural phase change in PZO upon electrical and thermal stimuli. a) Reciprocal space map of PbZrO3 440/280O and DyScO3 332O reflections showing epitaxial growth and the presence of ferroelastic domains in the epitaxial film. b) Polarization–electric field hysteresis response for epitaxial PbZrO3 film showing antiferroelectric switching. c) 2θ–ω XRD pattern for polycrystalline PbZrO3 film. d) Channeling-contrast backscatter electron micrograph of the polycrystalline PbZrO3 film. Arrows indicate the locations of clearly resolved ferroelastic domains. e) Phase diagram for lead zirconate titanate (PbZr1−xTixO3, PZT) constructed from ref. 27. f) Schematic of the dipole orientation in the antiferroelectric to ferroelectric (AFE-to-FE) and antiferroelectric to paraelectric (AFE-to-PE) phase transitions. credit: Kiumar Aryana et al, nature communication (2022). DOI: 10.1038/s41467-022-29023-Y
Researchers at the University of Virginia’s School of Engineering and Applied Science have found a way to create a versatile thermal conductor with the promise of more energy efficient electronic devices, green buildings and space exploration.
They have demonstrated that a known material used in electronic devices can now also be used as a thermal regulator, when in its very pure form. This new class of material gives engineers the ability to increase or decrease thermal conductivity on demand, turning a thermal insulator into a conductor and vice versa.
The team published its findings earlier this spring. nature communication, The paper is titled “Observation of solid-state bidirectional thermal conductivity switching in antiferroelectric lead zirconate.”
Bi-directional control or “tuning” of thermally conducting materials would be particularly useful in electronics and devices that need to operate in extreme temperatures or withstand extreme temperature fluctuations. One of the scenarios where equipment needs to perform in such harsh conditions is space.
“The temperature fluctuations in space can be very intense,” said Kiumar Aryana, who earned her Ph.D. in Mechanical and Aerospace Engineering at UVA this spring and is the first author of nature communication paper. “This type of thermal transport technology could be a huge advantage as we build vehicles and equipment for space exploration.”
“The Mars rover is a great example,” Aryna said. Ground temperatures at rover landing sites can reach 70 degrees Fahrenheit during the day and minus 146 degrees at night. To keep electronic components working through these wide temperature swings, the rover relies on an insulating box and heater to keep components from freezing and radiators from burning out.
“This new method of heat management is significantly less complex and means that heat regulation is easier to manage – and faster. Where it takes a long time for radiators or insulation to initiate heating or cooling, the solid-state mechanism will be nearly instantaneous. Being able to keep up with rapid temperature changes also makes things safer. Because heating and cooling can continue, the chances of a malfunction due to heat or cold are reduced – or worse – reduced goes,” Aaryana said.
Meanwhile, here on Earth, promising uses include the management of heating and cooling on a large scale, such as buildings, and on a smaller scale, such as circuit boards for electronics. Less energy equals green technology and lower cost.
This progress was supported by UVA Engineering’s materials science and engineering, and John Ehlefeld, associate professors of electrical and computer engineering, and Patrick E. A longstanding collaboration continues between Hopkins, the Whitney Stone Professor of Engineering, and Professor of Mechanical and Aerospace Engineering, and Aryna’s advisor.
The Ihlefeld-Hopkins team has over the course of a decade pioneered tunable thermal conductivity in crystalline materials, first at Sandia National Laboratories and now at UVA.
Tunability is unique to a class of functional materials called ferroelectrics, a feature of Ehlefeld’s multifunctional thin-film research group.
“A ferroelectric material is like a magnet; instead of a north and south pole, you have a positive and a negative charge,” Ehlefeld said. An electric field, or voltage, when applied to a ferroelectric material, “flips” the polarity of the material’s surface to its opposite state, where it remains until the opposite voltage is applied.
“Typically, thermal conductivity is considered a constant physical property,” Hopkins said. “If you want to convert a thermal conductor into an insulator, you have to permanently change its structure or integrate it with a new material.”
Prior research by Ehlefeld and Hopkins demonstrated how to reduce thermal conductivity with an electric field, and how to integrate materials within a device to increase thermal conductivity, but they could not make both the same material. .
For this project, the team used an antiferroelectric material in which both heat and voltage come into play.
Hopkins said, “What this interesting material does, in addition to being a high-quality crystal that has thermal conductivity trends similar to that of an amorphous glass, in addition to being solid-state, is that it allows us to change the thermal conductivity,” said Hopkins. Gives two unique knobs.” , “We can heat the crystal rapidly with a laser or apply voltage to actively tune the thermal conductivity and heat transport.”
“We tried using a commercial sample of lead zirconate to test for bi-directional thermal conductivity, but it didn’t work,” Aryana said. Len Martin, Chancellor Professor and Department Chair of Materials Science and Engineering at the University of California Berkeley, provided an extremely pure sample of lead zirconate. “Using Lane’s sampling, we achieved a 38% bi-directional change in thermal conductivity in a single explosion, which is a huge leap forward,” Aryana said.
Antiferroelectric material structures are bi-directional in nature. In the smallest repetition unit of a crystal lattice, one half has a polarity pointing up and the other half down, such that the positive and negative charges cancel each other out. When heated, the crystal structure changes and the antiferroelectricity goes away, which increases the thermal conductivity. Applying an electric field does the opposite – it causes the material to convert to ferroelectric and the thermal conductivity decreases. When the voltage is removed the net polarity becomes zero.
The flip in polarity and the arrangement of atoms in the crystals that support the antiferroelectric structure lead to observable and measurable thermal scattering phenomena – something like a heat signature – meaning that energy spreads through the material in the ways that it would. that can be predicted and controlled.
Members of Hopkins’ Experiments and Simulations in the Thermal Engineering Research Group have made many advances in laser measurements of materials. nature communication The paper presents an innovation in optical thermometry-based experiments in which students modified the antiferroelectric film through a transition from antiferroelectric to paraelectric structure, employing a third laser to bring about a rapid heating event, allowing it to be subjected to an applied electric current. Under gets the ability to be polarized. Farm.
For technologies to make an impact, engineers would need a large “on-off” switch to rapidly transfer or store a very large percentage of heat. The research team’s next steps include working to better define the material’s boundaries, so that they can create a new material with a high switching ratio, accelerating the use of actively tunable thermal conductivity materials .
Kiumars Aryana et al, Observation of switching solid-state bidirectional thermal conductivity in antiferroelectric lead zirconate (PbZrO3), nature communication (2022). DOI: 10.1038/s41467-022-29023-Y
Provided by University of Virginia School of Engineering and Applied Science
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Researchers harness the power of a new solid-state thermal technology
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