A new nanophotonic material has broken records for how stable it is at high temperatures. It could make it easier to make electricity and open up a lot of new ways to control and use thermal radiation.
The material, which is stable at temperatures of 2,000 degrees Fahrenheit in air and was created by a team of chemical and materials science engineers led by the University of Michigan, is a nearly two-fold improvement over current methods.
Shorter wavelengths can pass through the substance while infrared energy is reflected using a process known as destructive interference. By reflecting infrared waves back into the system, this may help reduce heat waste in thermophotovoltaic cells, which convert heat into electricity but cannot utilize infrared energy. The material can also be used for optical photovoltaics, thermal imaging, coatings that keep out the environment, sensing, and hiding from infrared surveillance equipment.
“It is comparable to how wave interference produces the color in butterfly wings. Although butterfly wings are made of colorless materials, they are patterned and structured in a way that causes some wavelengths of white light to be absorbed while others are reflected, giving the appearance of color. ” Andrej Lenert, who is an assistant professor of chemical engineering at the University of Michigan and a co-author of the study that was published in Nature Photonics, said,
“With infrared light, this substance performs a comparable function. Preventing the breakdown of that color-producing structure under intense heat has been the difficult part. ”
The method represents a significant departure from the state of engineered thermal emitters at the moment, which typically use ceramics and foams to control infrared emissions. Although they can withstand high temperatures, these materials have very little control over the wavelengths that they let through. Although previous attempts haven’t been stable at high temperatures, frequently melting or oxidizing, nanophotonics could provide much more control (the process that forms rust on iron). Furthermore, many nanophotonic materials can only remain stable in a vacuum.
By surpassing the previous mark for heat resistance among air-stable photonic crystals by more than 900 degrees Fahrenheit in open air, the new material contributes to the solution of that issue. The material is also tunable, allowing scientists to modify its energy for a wide range of potential applications. The research team says that adding this material to current TPVs will increase their efficiency by 10%, and they think that further improvements will lead to even bigger efficiency gains.
Combining their knowledge of chemical engineering and materials science, the team created the solution. The first step taken by Lenert’s chemical engineering team was to identify substances that wouldn’t mix even if they started to melt.
The objective, according to Lenert, is to find materials that will continue to maintain nice, crisp layers that reflect light in the desired manner even when conditions are extremely hot. “So, because they tend not to want to mix, we looked for materials with very different crystal structures.”
They postulated that a mixture of rock salt and the mineral perovskite, which is composed of calcium and titanium oxides, would work. Researchers from the Universities of Michigan and Virginia conducted supercomputer simulations to verify the combination’s viability.
The material was then meticulously deposited using pulsed laser deposition to produce precise layers with smooth interfaces by John Heron, co-corresponding author of the study and assistant professor of materials science and engineering at U-M, and Matthew Webb, a doctoral student in materials science and engineering. Instead of using conventional photonic materials, they chose oxides because they can be layered more precisely and are less likely to degrade in high heat. This made the nanophotonic material even more durable.
Heron stated that “in earlier work, conventional materials oxidized under high heat, losing their orderly layered structure.” However, this degradation has already essentially happened when starting with oxides. The final layered structure becomes more stable as a result.
Sean McSherry, the study’s first author and a doctoral student in materials science and engineering at the University of Michigan, used computer modeling to find hundreds of other combinations of materials that are also likely to work after testing demonstrated that the material performed as intended. The core discovery opens up a new line of research into other nanophotonic materials. This could help future researchers develop a variety of new materials for a wide range of uses, even though the material tested in the study probably won’t be used commercially for years.
