MIT researchers have developed a technique that enables real-time, 3D monitoring of corrosion, cracking, and other material failure processes inside a nuclear reactor environment.

This could allow engineers and scientists to design safer nuclear reactors that also deliver higher performance for applications like electricity generation and naval vessel propulsion.

During their experiments, the researchers utilized extremely powerful X-rays to mimic the behavior of neutrons interacting with a material inside a nuclear reactor.

They found that adding a buffer layer of silicon dioxide between the material and its substrate, and keeping the material under the X-ray beam for a longer period of time, improves the stability of the sample. This allows for real-time monitoring of material failure processes.

By reconstructing 3D image data on the structure of a material as it fails, researchers could design more resilient materials that can better withstand the stress caused by irradiation inside a nuclear reactor.

“If we can improve materials for a nuclear reactor, it means we can extend the life of that reactor. It also means the materials will take longer to fail, so we can get more use out of a nuclear reactor than we do now. The technique we’ve demonstrated here allows to push the boundary in understanding how materials fail in real-time,” says Ericmoore Jossou, who has shared appointments in the Department of Nuclear Science and Engineering (NSE), where he is the John Clark Hardwick Professor, and the Department of Electrical Engineering and Computer Science (EECS), and the MIT Schwarzman College of Computing.

Jossou, senior author of a study on this technique, is joined on the paper by lead author David Simonne, an NSE postdoc; Riley Hultquist, a graduate student in NSE; Jiangtao Zhao, of the European Synchrotron; and Andrea Resta, of Synchrotron SOLEIL. The research is published in the journal Scripta Materiala.

“Only with this technique can we measure strain with a nanoscale resolution during corrosion processes. Our goal is to bring such novel ideas to the nuclear science community while using synchrotrons both as an X-ray probe and radiation source,” adds Simonne.

Real-time imaging

Studying real-time failure of materials used in advanced nuclear reactors has long been a goal of Jossou’s research group.

Usually, researchers can only learn about such material failures after the fact, by removing the material from its environment and imaging it with a high-resolution instrument.

“We are interested in watching the process as it happens. If we can do that, we can follow the material from beginning to end and see when and how it fails. That helps us understand a material much better,” he says.

They simulate the process by firing an extremely focused X-ray beam at a sample to mimic the environment inside a nuclear reactor. The researchers must use a special type of high-intensity X-ray, which is only found in a handful of experimental facilities worldwide.

For these experiments they studied nickel, a material incorporated into alloys that are commonly used in advanced nuclear reactors. But before they could start the X-ray equipment, they had to prepare a sample.

To do this, the researchers used a process called solid state dewetting, which involves putting a thin film of the material onto a substrate and heating it to an extremely high temperature in a furnace until it transforms into single crystals.

“We thought making the samples was going to be a walk in the park, but it wasn’t,” Jossou says.

As the nickel heated up, it interacted with the silicon substrate and formed a new chemical compound, essentially derailing the entire experiment. After much trial-and-error, the researchers found that adding a thin layer of silicon dioxide between the nickel and substrate prevented this reaction.

But when crystals formed on top of the buffer layer, they were highly strained. This means the individual atoms had moved slightly to new positions, causing distortions in the crystal structure.

Phase retrieval algorithms can typically recover the 3D size and shape of a crystal in real-time, but if there is too much strain in the material, the algorithms will fail.

However, the team was surprised to find that keeping the X-ray beam trained on the sample for a longer period of time caused the strain to slowly relax, due to the silicon buffer layer. After a few extra minutes of X-rays, the sample was stable enough that they could utilize phase retrieval algorithms to accurately recover the 3D shape and size of the crystal.

“No one had been able to do that before. Now that we can make this crystal, we can image electrochemical processes like corrosion in real time, watching the crystal fail in 3D under conditions that are very similar to inside a nuclear reactor. This has far-reaching impacts,” he says.

They experimented with a different substrate, such as niobium doped strontium titanate, and found that only a silicon dioxide buffered silicon wafer created this unique effect.

An unexpected result

As they fine-tuned the experiment, the researchers discovered something else.

They could also use the X-ray beam to precisely control the amount of strain in the material, which could have implications for the development of microelectronics.

In the microelectronics community, engineers often introduce strain to deform a material’s crystal structure in a way that boosts its electrical or optical properties.

“With our technique, engineers can use X-rays to tune the strain in microelectronics while they are manufacturing them. While this was not our goal with these experiments, it is like getting two results for the price of one,” he adds.

In the future, the researchers want to apply this technique to more complex materials like steel and other metal alloys used in nuclear reactors and aerospace applications. They also want to see how changing the thickness of the silicon dioxide buffer layer impacts their ability to control the strain in a crystal sample.

“This discovery is significant for two reasons. First, it provides fundamental insight into how nanoscale materials respond to radiation—a question of growing importance for energy technologies, microelectronics, and quantum materials. Second, it highlights the critical role of the substrate in strain relaxation, showing that the supporting surface can determine whether particles retain or release strain when exposed to focused X-ray beams,” says Edwin Fohtung, an associate professor at the Rensselaer Polytechnic Institute, who was not involved with this work.

This story is republished courtesy of MIT News (web.mit.edu/newsoffice/), a popular site that covers news about MIT research, innovation and teaching.

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A salt called guanidinium thiocyanate can improve the efficiency and stability of perovskite solar cells, a new class of semiconductor that could make solar power cheaper and more powerful, according to researchers at UCL.

In a study published in the Journal of the American Chemical Society, the team showed that guanidinium thiocyanate can slow and control the way perovskite crystals form during fabrication, creating smoother and more uniform layers. This helps reduce the tiny flaws in the material that can hinder performance and shorten a cell’s lifespan.

Tandem perovskite cells—that is, two or more layers of solar cells stacked on top of each other—are seen as the future of ultra-efficient solar energy technology. That is because each layer can be tuned to absorb different parts of the solar spectrum, meaning they can convert more of that light into electricity. The new study used mixed tin-lead perovskites—typically the bottom layer of stacked cells.

Corresponding author Dr. Tom Macdonald (UCL Electronic & Electrical Engineering) said, “Our approach provides a straightforward, effective way to enhance perovskite quality during manufacturing, delivering solar cells that are both higher performing and more stable, key requirements for commercial success.”

In tests, the team achieved an efficiency of 22.3% for this material, close to the best reported for mixed tin-lead perovskites. For comparison, the best silicon solar cells in the lab have reached around 27% efficiency, while most commercial panels installed on rooftops today deliver about 22%. All-perovskite tandem devices (that is, using more than one layer of perovskite cell) have already surpassed 30% in the lab, highlighting their potential to achieve a step-change in solar power generation.

Using salt as demonstrated by the UCL team for the bottom layer of tandem cells—either guanidinium thiocyanate or potentially another agent—would likely increase this world-record efficiency further.

Perovskite solar cells are already known for their tolerance to defects, but reducing those defects as far as possible is key to unlocking higher efficiencies and longer-lasting devices. The guanidinium additive works by giving researchers greater control over crystal growth, limiting the imperfections that occur when the material forms too quickly.

First author Yueyao Dong (UCL Electronic & Electrical Engineering) said, “This work gave us valuable insight into the crystal formation process. By modulating it in a controlled way, we were able to create much higher-quality films—a change that directly translates into more efficient and longer-lasting devices.”

Co-author Dr. Chieh-Ting Lin (National Chung Hsing University) added, “It opens the door to fine-tuning the structure of perovskites for high-performance tandem solar cells, with the potential to significantly push the limits of efficiency.”

Perovskite solar cells have emerged over the past decade as a leading alternative to traditional silicon-based solar panels. Like silicon, perovskites are semiconductors—materials that can conduct electricity under certain conditions.

An advantage of perovskites is that they can be made at low temperatures using simpler, less energy-intensive processes. This makes them attractive for large-scale manufacturing and opens possibilities for lightweight, flexible solar panels.

Perovskite cells can also be tuned to capture different parts of the solar spectrum, making them ideal for tandem solar cells. Tandem cells can either combine perovskite with silicon to harvest more sunlight, or be configured as all-perovskite tandems, which offer enhanced light-harvesting tunability and greater manufacturing flexibility.

While guanidinium salts have been used in perovskite research before, this study provides new insight into how they influence crystal formation and how this can lead to more efficient and stable solar cells. The work builds on earlier research by the team, published in ACS Energy Letters, which showed that guanidinium can also help improve charge transport and reduce the unwanted movement of ions within the cell.

As the demand for clean energy grows, the ability to manufacture high-efficiency, low-cost solar cells at scale will be crucial. Advances like these could help overcome the remaining roadblocks to commercializing perovskite technology, opening the way for next-generation solar panels that are more efficient, more durable and more affordable.