Superfast Cooling Explores New Abilities for Promising Next Generation Optoelectronic Materials

Virtually any material that melts can potentially be turned into a glass—it just needs to be cooled down fast enough. While the age-old method of dunking a glowing hot object into a vat of water can get the job done, that isn’t an option for more delicate materials.

At Duke University, researchers are exploring possibilities opened by a new instrument called a Flash Differential Scanning Calorimeter (Flash-DSC), which allows them to cool materials at an unprecedented rate of up to three million degrees Celsius per minute. While that may sound like overkill, it isn’t—those speeds are necessary to stop certain materials from forming crystals instead.

“The conventional systems in my previous labs have a calorimeter that can cool things to a very limited temperature and at sluggish rates,” explained Akash Singh, a PhD student in mechanical engineering and materials science at Duke. “When we wanted to study perovskites, we were limited because we could not cool it beyond 50 degrees Celsius per minute.”

Perovskites are a class of compounds that have gained significant attention in the field of materials science due to their unique properties, particularly in the area of solar cells, LEDs and sensors. Besides the specific molecular recipes used to create them, perovskites’ properties are largely determined by their molecular structure as well.

Perovskites naturally want to form crystalline structures, which are defined by how their atoms are arranged in a highly organized structure or lattice. When a crystalline material melts and is allowed to cool slowly, the atoms have time to return to their original lattice positions. Ice is a great everyday example, as its water molecules freeze back into that grid-like structure when cooled.

When a material is cooled rapidly, however, its atoms don’t have enough time to organize themselves into a regular lattice. Instead, they form a disordered structure, resulting in a glass. That disorder can lead to exciting new properties for a given material. But obtaining that disorder can be extremely difficult.

Enter the Flash-DSC.

“The Flash-DSC tool allows us to rapidly cool any melted material in a super-fast fashion,” Singh said. “That potentially allows us to stabilize those glassy phases that were impossible in the conventional laboratory setting, while only requiring nanograms of sample materials to study— hundreds of thousands of times less than what conventional DSC tools require.”

Over the past five years, Singh has worked under the guidance of David Mitzi, the Simon Family Distinguished Professor of Mechanical Engineering and Materials Science at Duke, to explore the capabilities and possibilities provided by glassy perovskites—something that has not been explored in over 130 years of perovskite semiconductor research. Their findings have since been published in high-impact journals from the American Chemical Society (J. Am. Chem. Soc. 2023, 145, 18623-18633.) to the Royal Society of Chemistry (Chem. Sci., 2024, 15, 6432-6444).

Their results are far-reaching. Glassy perovskites enable access to multiple configurational arrangements leading to versatile characteristics such as lower thermal or electrical conductivity, improved catalytic activity, reduced sensitivity to imperfections, and increased longevity. Also, glass can be fabricated in diverse form factors that are hard to form for crystalline counterparts, including monolithic slabs, thin films and fibers.

But perhaps their most interesting quality is the ability to transition back and forth between glass and crystalline states. Because each offers unique properties, this switching could underline cost-effective memory, computing, communication, photonic and sensing applications.

The recently commissioned Flash-DSC tool in Mitzi’s lab also has broad potential to help understand ultrafast phase change phenomena and stabilize metastable phases in other fields, too. Researchers working on diverse materials beyond hybrid perovskites such as polymers, pharmaceuticals and advanced semiconducting alloys could benefit from the ability to study phase changes at such extreme cooling and heating rates.

Singh emphasizes that the tool should aid in fostering intra- and inter-university collaboration among researchers across fields like chemistry, physics and materials science and could lead to significant advances in the study of materials properties at large.

The Flash-DSC instrument is supported through funding from the National Science Foundation under Grant No. DMR- 2114117.