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FRIPRO-Fri prosjektstøtte

Quasicrystal nucleation in a metallic matrix

Alternative title: Kvasikrystaller kimdannet fra fast løsning i et metallgitter

Awarded: NOK 12.0 mill.

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Project Period:

2021 - 2025

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The quasicrystal (QC) was discovered in 1982. Daniel Shechtman used transmission electron microscopy (TEM) on an aluminium (Al) alloy with 14% manganese. He found particles with 5-fold symmetry. This is impossible for normal crystals, where atoms line up with periodic intervals. Instead, he found their separation increased by the golden ratio, t~1.618. More crystals with other 'forbidden' symmetries were soon found. Textbooks were rewritten. Shechtman received the Nobel Prize in Chemistry in 2011. How quasicrystals form on the atomic scale is still a mystery. This project uses a new strategy: We study how QC forms within the Al crystal lattice. When an alloy cools, the alloying elements also become locked in the Al lattice. Empty sites, vacancies, always exist. They give atoms possibilities for moving. Together with Al, these foreign atoms initially form small clusters on the lattice. Later, larger crystals called 'precipitates' form. In 2023 we have made progress in understanding the structural connections between quasicrystalline precipitates and quasicrystalline approximants in Al alloys. The PhD student in the project presented results from the project at the International Union of Crystallography congress.

The project will obtain fundamental knowledge about quasicrystal formation and growth from supersaturated solid solution. Two material systems are selected: Al-Mn-Si-(Cr) and Al-Mg-Cu-(Ag). The novel approach implies solving atomic structure of quasicrystal at selected growth stages in close reference to the Al host lattice. State-of-the-art analysis methods (Transmission Electron Microscopy and Atom Probe Tomography) will be used to image the smallest quasicrystal building blocks (molecular units), their subsequent aggregates, and the final quasicrystal phases after selected heat treatments. The techniques offer sufficient resolution that atomic models of the small aggregates can be made at each stage, together with the surrounding host. The project also has a novelty aspect related to use of Scanning Precession Electron Diffraction on small quasicrystal precipitates in a host lattice. Ab-initio quantum mechanical calculations will be used to test the structure models of the different stages. These calculations will be based on a novel on-the-fly machine learning force field methodology. The lattice kinetic Monte Carlo technique will be applied to model the time evolution of the QC growth. Results will be compiled into an experimentally verified set of growth rules for quasicrystals, a final sub-goal for the project. The most critical milestone for the project is the final validation of the selected materials' suitability for the study in terms of the kinetics of the quasicrystal formation.

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FRIPRO-Fri prosjektstøtte

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