Research ArticleMATERIALS SCIENCE

Picosecond amorphization of SiO2 stishovite under tension

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Science Advances  12 May 2017:
Vol. 3, no. 5, e1602339
DOI: 10.1126/sciadv.1602339
  • Fig. 1 Rapid amorphization of stishovite under tension.

    (A) Simulation cell at ρ = 4.1 g/cm3. The yellow and red spheres are Si and O atoms, respectively. (B) Time evolution of the pressure. Inset: Final pressure for each strain value. (C and D) Snapshots of single-crystalline stishovite at t = 7.05 ps (C) and amorphized SiO2 at t = 9.06 ps (D).

  • Fig. 2 Stishovite-to-amorphous transformation.

    (A) Energy-density relation obtained by QMD simulations. The energy is relative to the minimum energy of single-crystalline stishovite. The solid black circles denote the stishovite crystalline phase, whereas the open blue squares are the amorphous phase. The amorphous-phase data points denoted by open and solid squares are obtained by QMD simulations with and without temperature control, respectively. The results labeled (b) and (e) are obtained by simulations that start from the atomic configurations of (c) and (d) by changing the mass density to ρ = 3.4 and 2.4 g/cm3, respectively. The solid red triangles are obtained by gradually changing the volume from that of the atomic configuration (f). The solid green triangles denote normal amorphous silica prepared by a melt-quench procedure. The black, red, and green curves show fitting using a third-order BM-EoS. (B) Pressure-density relation obtained by QMD simulations for the stishovite (solid black circles) and amorphous (solid blue squares and solid red triangles) phases. The black and red curves are the derivative of the BM-EoS curves in (A) with respect to volume, respectively, for the stishovite and amorphous phases. (C to F) Mass-density dependence of partial pair distribution function gSiO(r). (G to J) Mass-density dependence of bond-angle distributions θSi-O-Si and θO-Si-O.

  • Fig. 3 Tension-derived high-density amorphous silica.

    (A to C) Average coordination number distributions as a function of density for Si atoms with cutoff distance rSi-O = 2.2 Å. (D to F) Snapshots of a SiO4 tetrahedral unit (D), SiO5 pyramidal unit (E), and SiO6 octahedral unit (F). The yellow and red spheres are Si and O atoms, respectively, whereas the polygonal surfaces are represented by yellow planes. (G to I) Snapshots of local structures found in the intermediate amorphous structure formed by three SiOx units sharing O atoms: three corner-sharing tetrahedra (G), a pair of edge-shared tetrahedra (each sharing a corner with a pyramid) (H), and a corner-sharing tetrahedron-pyramid pair (each sharing an edge with another pyramid) (I).

  • Fig. 4 Amorphization pathways.

    (A) Energy profile from stishovite crystal (reaction coordinate λ = 0) to high-density amorphous phase (λ = 1) obtained by NEB calculation. The energy for configuration 0 is set to zero. (B) Energy profile for a subsequent amorphous-to-amorphous transformation corresponding to configurations (d) to (e) in Fig. 2A. (C and D) Distributions of the coordination number of Si (C) and O (D) atoms along the reaction pathway, which are calculated using a cutoff distance rSi-O = 2.2 Å. (E to H) Snapshots of atomic configurations at λ = 0 (E), 0.33 (F), 0.67 (G), and 1 (H) along the stishovite-to-amorphous transformation at ρ = 3.4 g/cm3, corresponding to a transition from (a) to (b) that is shown in Fig. 2A.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/3/5/e1602339/DC1

    movie S1. Rapid amorphization of stishovite upon volume expansion at a critical tension of −30 GPa.

    movie S2. Change of atomic configurations along the reaction pathway from the stishovite to amorphous phases at ρ = 3.4 g/cm3.

    fig. S1. Si-Si and O-O pair distributions at various densities.

    fig. S2. Change of coordination numbers and bond-angle distributions during the stishovite-to-amorphous transformation.

    fig. S3. Atomic displacements during the stishovite-to-amorphous transformation.

  • Supplementary Materials

    This PDF file includes:

    • Legends for movies S1 and S2
    • fig. S1. Si-Si and O-O pair distributions at various densities.
    • fig. S2. Change of coordination numbers and bond-angle distributions during the stishoviteto-amorphous transformation.
    • fig. S3. Atomic displacements during the stishovite-to-amorphous transformation.

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    Other Supplementary Material for this manuscript includes the following:

    • movie S1 (.mov format). Rapid amorphization of stishovite upon volume expansion at a critical tension of −30 GPa.
    • movie S2 (.mov format). Change of atomic configurations along the reaction pathway from the stishovite to amorphous phases at ρ = 3.4 g/cm3.

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