Discovery of 13-atom clusters could mean control in manufacturing materials far-from-equilibrium

In their latest research, the Shahani group upends conventional wisdom by showing that quasicrystals grow dendritically from a solid phase precursor, not just under a liquid-to-solid transition.
Discovery of 13-atom clusters could mean control in manufacturing materials far-from-equilibrium

Asst. Professor Ashwin Shahani. Periodic crystalline (approximant) structures evolve into quasicrystalline structures and the interface between the quasicrystal and approximant supports the formation of dendrites (tree-like structures).

Quasicrystals, or “nature’s forbidden crystals” as they are sometimes called, are structures that are ordered but aperiodic. Their formation has been a long-standing puzzle in condensed matter physics since their discovery in 1984. This is because the growth of metastable quasicrystals is inaccessible using conventional imaging approaches. 

In a new paper published in Physical Review Letters, Assistant Professor Ashwin Shahani’s group tracks in situ the solid‑state formation of metastable and dendritic quasicrystals. On the basis of their time‑resolved experiments and supporting molecular dynamics simulations, they provide an atomic picture of how periodic crystalline (approximant) structures evolve into quasicrystalline structures in terms of their structural similarity and how the interface between the quasicrystal and approximant supports the formation of dendrites (tree-like structures). Ultimately, they show that a 13-atom icosahedral motif is dominant upon rapid annealing, and if a sufficient population of these motifs exist, they could guide phase selection. Such motifs are the essential building blocks for quasicrystal growth from a solid or a liquid precursor. 

We asked Assistant Professor Shahani more about his latest findings.

How is this research related to your previous work regarding quasicrystal growth?

In this work, we study not the growth of quasicrystals from the liquid phase, but rather from a parent solid phase. We show that the quasicrystals grow in the shape of dendrites, or tree-like structures, which goes against our conventional wisdom. Theory tells us that dendrites should predominantly form under a liquid-to-solid transition, and yet we see dendrites in the solid-state.  

Why do you think the work you're doing is important?

In order to control structure in manufacturing metallic materials far-from-equilibrium, we need to understand at a very fundamental level where that structure comes from. This is the processing-structure paradigm of materials science. In this case, the solid dendritic quasicrystals “inherit” the structure of the parent solid phase.  

What were the most important discoveries and how did you arrive at them?

The important discovery was that of 13-atom clusters that facilitate the transition from one periodic phase to a quasicrystalline phase. These “building blocks” are key to the solid-state phase transition, and they also enable the growth of dendritic instabilities. The clusters are in the shape of icosahedra, which look like 20-sided dice. Their existence holds broad implications to the stability of phases and interfaces.  

What were the technological barriers to making this project work?

It is notoriously difficult to capture the growth of quasicrystals under far-from-equilibrium conditions via conventional probes and in real-time. That is because it unfolds too rapidly under small spatial scales. To meet the challenge, we imaged the transient growth dynamics at microsecond time-scales via dynamic transmission electron microscopy at Lawrence Livermore National Laboratory.  

Did anything surprise you during this project? Anything that didn't play out the way you expected?

 Believe it or not, this particular experiment was an accident! We were hoping to visualize the liquid-to-solid transition, but instead we captured only solid-state growth patterns. Our laser power was not high enough to melt our thin film samples. Research is often the product of serendipity, and this is a prime example.

Ten years from now, how might the world be different because of this research?

The growth mechanism that we have uncovered suggests that 13-atom clusters guide phase selection, which will in turn allow us to better predict and control the manufacture of metallic materials far-from-equilibrium, for a range of future applications.

 

The paper is titled “Dynamic Observation of Dendritic Quasicrystal Growth upon Laser-induced Solid-state Transformation.” Researchers on the project also included Insung Han (Shahani group, now at Oxford University), Joseph T. McKeown (Lawrence Livermore National Laboratory), Ling Tang (Zhejiang University of Technology, Hangzhou, China), Cai-Zhuang Wang (Ames Laboratory and Iowa State University), Hadi Parsamehr (Shahani group), Zhucong Xi (Shahani group), Ying-Rui Lu (National Synchrotron Radiation Research Center, Hsinchu, Taiwan), and Matthew J. Kramer (Ames Laboratory). 

The research was funded by the U.S. Department of Energy (DOE), Office of Science, Office of Basic Energy Sciences, under Award No. DE-SC0019118. Work at Lawrence Livermore National Laboratory (LLNL) was performed under the auspices of the U.S. DOE under Contract DE-AC52-07NA27344. Work at LLNL was supported by the Laboratory Directed Research and Development Program under project tracking code 18- SI-003. The research performed at the Ames Laboratory, which is operated for the U.S. DOE by Iowa State University, under contract No. DE-AC02-07CH11358 was funded by the U.S. DOE, Office of Science, Basic Energy Sciences, Materials Science and Engineering Division.