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Picosecond amorphization of SiO2 stishovite under tension

Masaaki Misawa,Emina Ryuo,Kimiko Yoshida,R. Kalia,A. Nakano,N. Nishiyama,F. Shimojo,P. Vashishta,F. Wakai

Published 2017 in Science Advances

ABSTRACT

Quantum simulation reveals that fast tensile amorphization is key to hard and tough ceramics made of Earth-abundant silica. 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.

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