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Sci Adv. 2017 May 12;3(5):e1602339. doi: 10.1126/sciadv.1602339. eCollection 2017 May.

Picosecond amorphization of SiO2 stishovite under tension.

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Collaboratory for Advanced Computing and Simulations, Department of Physics and Astronomy, Department of Computer Science, Department of Chemical Engineering and Materials Science, and Department of Biological Sciences, University of Southern California, Los Angeles, CA 90089-0242, USA.
Department of Physics, Kumamoto University, Kumamoto 860-8555, Japan.
Materials and Structures Laboratory, Tokyo Institute of Technology, 4259 Nagatsuta, Midori, Yokohama 226-8503, Japan.
Deutsches Elektronen-Synchrotron (DESY), Hamburg 22607, Germany.


It is extremely difficult to realize two conflicting properties-high hardness and toughness-in one material. Nano-polycrystalline stishovite, recently synthesized from Earth-abundant silica glass, proved to be a super-hard, ultra-tough material, which could provide sustainable supply of high-performance ceramics. Our quantum molecular dynamics simulations show that stishovite amorphizes rapidly on the order of picosecond under tension in front of a crack tip. We find a displacive amorphization mechanism that only involves short-distance collective motions of atoms, thereby facilitating the rapid transformation. The two-step amorphization pathway involves an intermediate state akin to experimentally suggested "high-density glass polymorphs" before eventually transforming to normal glass. The rapid amorphization can catch up with, screen, and self-heal a fast-moving crack. This new concept of fast amorphization toughening likely operates in other pressure-synthesized hard solids.


Amorphization; high-density glass; nano-polycrystal; quantum molecular dynamics; stishovite; toughening

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