Heat-Resistant Material Eyed for Novel Electronic Applications

Researchers have developed a new nanophotonic material that they said has demonstrated unprecedented heat resistance, paving the way for more efficient energy production as well as new possibilities for controlling and converting thermal radiation.

A team at the University of Michigan developed the material, which uses a phenomenon called destructive interference to reflect infrared energy while letting shorter wavelengths pass through. In this way, the material controls the flow of infrared radiation, thus remaining stable at temperatures of 2000 degrees Fahrenheit in air—nearly a twofold improvement over existing material approaches, researchers said.

Andrej Lenert, an assistant professor of chemical engineering who co-led the study, compared how the phenomenon works to how a butterfly's wings are composed of materials with no color, but use wave interference to appear colorful to the eye. “Those materials are structured and patterned in a way that absorbs some wavelengths of white light but reflects others, producing the appearance of color,” he said in an article posted to Michigan News.

The material does something similar with infrared energy, Lenert said. However, until now researchers had not been able to harness this effect. "The challenging part has been preventing breakdown of that color-producing structure under high heat," he said in the article.

Changing the Materials Game

Historically, scientists have used foams and ceramics to limit a material's infrared emissions, producing materials that are stable at high temperature but have very limited control over which wavelengths can pass through them. The researchers' approach here to use nanophotonics, then, is a significant departure from the current state of engineered thermal emitters, promising much more tunable control, they said.

However, in the past, attempts using similar technology have produced materials that lacked stability at high temperatures, resulting in melting or oxidizing. Moreover, many nanophotonic materials only were able to maintain their stability in a vacuum and not in air. To solve this problem, researchers combined two scientific disciplines—chemical engineering and materials science. They began their search for a suitable material by identifying ones that wouldn't mix even if they started to melt, Lenert said.

“The goal is to find materials that will maintain nice, crisp layers that reflect light in the way we want, even when things get very hot,” he said in the article. “So we looked for materials with very different crystal structures, because they tend not to want to mix.”

Finding the Right Combination

Researchers eventually decided that a combination of rock salt and perovskite—a mineral made of calcium and titanium oxides that's becoming well-known for its use in photovoltaics—may be what they're looking for. To confirm this hypothesis, researchers at both at the University of Michigan and the University of Virginia ran supercomputer simulations.

The team then used pulsed laser deposition to deposit the material in such a way as to achieve precise layers with smooth interfaces. To make it even more durable, they used oxides—which can be layered more precisely and are more robust in high heat—rather than photonic materials, researchers said

“In previous work, traditional materials oxidized under high heat, losing their orderly layered structure,” explained John Heron, an assistant professor of materials science and engineering at the University of Michigan who co-led the research with Lenert. “But when you start out with oxides, that degradation has essentially already taken place. That produces increased stability in the final layered structure.”

Researchers published a paper on their work in the journal Nature Nanotechnology. They report a resulting material that improves the previous record for heat resistance among air-stable photonic crystals by more than 900 degrees Fahrenheit in open air, researchers said. The material also is tunable, which will allow researchers to tweak it to modify energy for a wide variety of potential applications.

For example, the material's use of the phenomenon could potentially reduce heat waste in thermophotovoltaic cells—which convert heat into electricity but can’t use infrared energy—by reflecting infrared waves back into the system, researchers said.

Other areas in which the material could be applicable include optical photovoltaics, thermal imaging, environmental barrier coatings, sensing, and camouflage from infrared surveillance devices, they added.