Utilizing cutting-edge microscopy technology at UC Irvine's Materials Research Institute, the research team heated platinum nanocrystalline thin films to observe grain rotation mechanisms in unparalleled detail. The results, recently published in 'Science', mark a major step in understanding the atomic processes within these materials.
The researchers employed advanced four-dimensional scanning transmission electron microscopy (4D-STEM) and high-angle annular dark-field STEM to capture real-time atomic activities. They developed a machine learning algorithm to analyze the vast datasets produced by these tools, allowing them to focus on the role of disconnections at grain boundaries, critical points where imperfections occur.
"Scientists have speculated and theorized on phenomena occurring at the boundaries of crystalline grains for decades, but now - through the use of the most advanced instruments available to the scientific community - we have been able to transition from theory to observation," said lead author Xiaoqing Pan, UC Irvine Distinguished Professor of materials science and engineering and director of the UC Irvine Materials Research Institute.
Grain boundaries, where individual crystal grains meet, are known to affect material conductivity and efficiency. The team discovered that grain rotation occurs through the propagation of disconnections-defects that combine both step and dislocation features-along these boundaries. This provides new insights into the evolution of nanocrystalline materials.
The study also revealed, for the first time, a statistical correlation between grain rotation and grain growth or shrinkage. This relationship, driven by disconnection motion, was confirmed through real-time STEM observations and atomistic simulations. This breakthrough sheds light on how grain boundaries evolve, offering deeper insights into the behavior of polycrystalline materials.
"Our results provide unequivocal, quantitative, and predictive evidence of the mechanism by which grains rotate in polycrystals on an atomic scale," said Pan. "Understanding how disconnections control grain rotation and grain boundary migration processes can lead to new strategies for optimizing the microstructures of these materials. This knowledge is invaluable for advancing technologies in various industries, including electronics, aerospace, and automotive sectors."
The findings from this research offer potential avenues for enhancing the durability and efficiency of polycrystalline materials, which are key to the future of electronics, energy systems, and more.
Research Report:Grain rotation mechanisms in nanocrystalline materials: Multiscale observations in Pt thin films
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UC Irvine Materials Research Institute
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