Materials Science

Pressure-Packed Partnerships

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Science  30 Aug 2002:
Vol. 297, Issue 5586, pp. 1447
DOI: 10.1126/science.297.5586.1447c

If a solid is squeezed hard enough, it can be forced to undergo a phase transition, with accompanying changes in the arrangement of atoms. For example, crystalline silica can go from a fourfold-coordinated Si to a sixfold coordination, and the two new Si-O bonds that form cause the stishovite phase to remain stable when the pressure is removed.

Using molecular dynamics simulations, Trachenko and Dove look at the mechanics of high-pressure deformation of amorphous silica. At low pressures, the densification is reversible, and atoms in different regions of the sample undergo large local motions in response to changes in applied pressure. Above 3 gigapascals, however, an irreversible increase in the coordination of some of the Si atoms occurs, and this is enhanced with increasing temperature. They also observed a second process, where existing Si-O bonds are broken and new Si-O partnerships form, accompanied by a change in the local topology with an increase in the Si coordination and the formation of small rings of linked polyhedra. — MSL

J. Phys. Condens. Matter14, 7449 (2002).

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