The key to beating the heat is degrading the materials in advance — ScienceDaily

A new nanophotonic material has broken records for high-temperature stability, potentially ushering in more efficient power generation and opening a host of new possibilities in the control and conversion of thermal radiation.

Developed by a team of chemical and materials science engineers led by the University of Michigan, the material controls the flow of infrared radiation and is stable in air at temperatures of 2,000 degrees Fahrenheit, a nearly two-fold improvement over existing approaches.

The material uses a phenomenon called destructive interference to reflect infrared energy while allowing shorter wavelengths to pass. This could potentially reduce heat wastage in thermophotovoltaic cells, which convert heat into electricity but cannot harness infrared energy by reflecting infrared waves back into the system. The material could also be useful in optical photovoltaics, thermal imaging, environmental barrier coatings, sensors, camouflage from infrared surveillance devices, and other applications.

“It’s similar to the way butterfly wings use wave interference to get their color. Butterfly wings are made of colorless materials, but these materials are structured and patterned to absorb some wavelengths of white light but reflect others, thus creating the appearance of color,” said Andrej Lenert, UM assistant professor of chemical engineering and co-author of the study in nature photonics.

“This material does something similar with infrared energy. The challenge is to prevent this color-producing structure from collapsing under high heat.”

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The approach is a major departure from the current state of engineered radiant heaters, which typically use foams and ceramics to limit infrared emissions. These materials are stable at high temperatures, but offer very limited control over which wavelengths they let through. Nanophotonics could offer much more tunable control, but previous efforts have not been stable at high temperatures, as they often melt or oxidize (the process that forms rust on iron). In addition, many nanophotonic materials only retain their stability in a vacuum.

The new material works to solve this problem, beating the previous record for heat resistance among air-stable photonic crystals by more than 900 degrees Fahrenheit outdoors. In addition, the material is tunable, allowing researchers to tweak it to modify the energy for a variety of potential applications. The research team predicted that applying this material to existing TPVs will increase efficiency by 10% and believe that much larger efficiency gains are possible with further optimization.

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The team developed the solution by combining expertise in chemical engineering and materials science. Lenert’s chemical engineering team began searching for materials that would not mix even if they began to melt.

“The goal is to find materials that retain nice, crisp layers that reflect light the way we want it to, even when it gets really hot,” Lenert said. “So we looked for materials with very different crystal structures because they tend not to mix.”

They hypothesized that a combination of rock salt and perovskite, a mineral composed of oxides of calcium and titanium, fit the bill. Researchers at UM and the University of Virginia ran supercomputer simulations to confirm the combination was a good choice.

John Heron, co-corresponding author on the study and an assistant professor of materials science and engineering at UM, and Matthew Webb, a graduate student in materials science and engineering, then carefully deposited the material using pulsed laser deposition to achieve precise and smooth layers at the interfaces. To make the material even more durable, they used oxides instead of traditional photonic materials; The oxides can be layered more precisely and are less likely to degrade at high heat.

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“In previous work, traditional materials oxidized under high heat and lost their ordered layered structure,” Heron said. “But if you start with oxides, essentially that degradation has already taken place. This leads to increased stability in the final layered structure.”

After tests confirmed the material worked as designed, Sean McSherry, first author of the study and a graduate student in materials science and engineering at UM, used computer models to identify hundreds of other material combinations that also likely work. While commercialization of the material tested in the study is likely years away, the core discovery opens a new research direction into a variety of other nanophotonic materials that could help future researchers develop a range of new materials for a variety of applications.

The research was supported by the Department of Defense, Defense Advanced Research Projects Agency, grant number HR00112190005.

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