Simulating the amorphization of α-quartz under pressure

Abstract

Extensive molecular-dynamics simulations have been performed within a classical force-field model for the pressure-induced amorphization of quartz. In agreement with earlier molecular-dynamics studies, we find that a phase transition occurs within the experimental pressure range of the amorphization transformation. However, at variance with previous interpretations, we find that the resulting phase is not amorphous. The correlation functions of the equilibrated structure can be shown to be consistent with those of a crystalline phase. Two transformations to ordered structures occur sequentially during the simulations. The first transformation is likely to be related to the recently discovered transition of quartz to an intermediate crystalline phase before its amorphization. The second transformation, instead, yields a compact octahedrally coordinated Si sublattice. The latter structure may be an artifact of the classical force field.

The structure of amorphous, crystalline and liquid GeO2

“…The structure obtained at this pressure appears to be quite similar to the structure calculated for SiO 2 at 21.5 GP a [112]. Furthermore it is shown that α-quartz-like GeO 2 close to the transition is mechanically unstable as some of the elastic moduli of the lattice become negative.…”

Surface photometry of new nearby dwarf galaxies

“…There is a noticeable separation in the M − µ diagram between galaxies of different morphological types. It was suggested by Binggeli (1994) that the M − µ diagram for stellar systems might be the equivalent of the HR diagram for stars (see Fig. 1 of his review).…”

Galaxy And Mass Assembly (GAMA): the unimodal nature of the dwarf galaxy population

“…The BBD showing the natural morphological segregation of Virgo cluster galaxies in the space mapped by central surface brightness and absolute magnitude has been shown by several authors (Caldwell 1983;Binggeli, Sandage, & Tarenghi 1984;Kormendy 1985;Binggeli 1994). From these seminal works, in Binggeli's words, "The M − µ diagram for stellar systems might well become the equivalent of the HR diagram for stars".…”