An international team that included scientists from the Department of Energy's Oak Ridge National Laboratory used neutron scattering , X-ray diffraction and high-resolution digital modeling to discover a simpler, cheaper way to create a prized form of silicon not found in nature.
The results hold promise for energy storage and electronics production.
"This question has been a long-standing problem in materials science, and 10 years of research have gone just into this project," said Stephan Irle, an ORNL senior computational scientist and co-author of the study published in Materials Today. "This method would achieve tremendous energy savings and should be highly scalable for industry."
Silicon, the most abundant material on the planet after oxygen, offers efficient conductivity at low costs for various forms of batteries. R8, a rare form of silicon so far produced only under laboratory conditions, offers even greater flexibility and higher efficiency.
Because R8 doesn't occur in nature, scientists previously produced it only by crushing crystalline silicon at extreme pressure - an expensive, complicated and time-consuming process.
The research team, led by Bianca Haberl, an associate professor of physics at Australian National University in Canberra and former staff scientist at ORNL's Spallation Neutron Source , sought to find an alternate way. The answer lay in density matching, which occurs when materials align perfectly by density and naturally organize themselves.
"You could imagine it as autonomous building blocks that sort themselves out and come together into just the right pattern," Irle said.
The team found amorphous silicon - a disordered, glassy version of the element that's easier to produce due to its simpler structure - could be compressed at room temperature under pressures roughly 25 percent lower than traditional methods to reach the necessary density level, known as a medium-density amorphous state. As the amorphous silicon compresses, its jumbled structure realigns into the crystalline structure of R8.
The research team used neutron diffraction at SNS and X-ray diffraction at Argonne National Laboratory's Advanced Photon Source to measure density-driven transformations in silicon in real time. The unique tools and capabilities of the SNS and APS, both DOE Office of Science user facilities, captured the necessary details of the process for the team to reproduce the transformation digitally.
The team ran simulations of the data on ORNL's Compute and Data Environment for Science high-performance computing cluster to model various methods under a wide range of conditions in detail.
"We tried to figure out all the available approaches for modeling the R8 phases and screen for the best one," said Gang Seob Jung, an ORNL research scientist and co-author of the study. "The modeling was key to demonstrating that what we observed was accurate and scientifically sound."
The modeling showed the disordered nature of the amorphous silicon gave the material enough structural flexibility to bypass the rigid pathways followed by crystalline materials. That flexibility allowed the starting amorphous material to bypass the usual complex pathway through various metallic phases and take a direct shortcut to the desired R8 structure. The team demonstrated this density-matching principle worked not just for silicon but for germanium , a sister element used in fiber optics and other electronics systems.
"With further exploration, we may determine this method can be used for other important materials as well," Irle said.
Besides Haberl, Irle and Jung, the research team included Malcolm Guthrie and Jamie Molaison of ORNL, Leonardus B. Bayu Aji of Lawrence Livermore National Laboratory, Guoyin Shen of Argonne, and Jodie Bradby of ANU.
This research was supported by the DOE Office of Science's Advanced Scientific Computing Research program, the National Nuclear Security Administration's Office of Experimental Sciences, the National Science Foundation and the Australian Research Council. SNS and APS are DOE Office of Science user facilities.
Versions of this story were originally published by Argonne and ANU .
UT-Battelle manages ORNL for DOE's Office of Science, the single largest supporter of basic research in the physical sciences in the United States. DOE's Office of Science is working to address some of the most pressing challenges of our time. For more information, visit https://energy.gov/science . - Matt Lakin
