Materials Science

Feeling the Squeeze

See allHide authors and affiliations

Science  01 Oct 2004:
Vol. 306, Issue 5693, pp. 23
DOI: 10.1126/science.306.5693.23b

Under high pressure, atoms in a crystal may rearrange into a more favorable crystal structure or may lose order and become amorphous. Perhaps less well appreciated is that the same can occur in glasses, which show only short-and intermediate-range ordering; these are much harder to study, and there is still debate as to whether the transitions are discrete or continuous.

Guthrie et al. have examined the behavior of germanium dioxide, a classic network-forming glass, using in situ x-ray diffraction to examine the Ge-Ge and Ge-O correlations, and neutron scattering to look at O-O correlations, as well as molecular dynamics simulations. At ambient pressure, GeO2 forms a standard tetrahedral glass with fourfold Ge-O coordination, and at a pressure of 15 gigapascals they observed a fully octahedral glass with sixfold Ge-O coordination. However, at intermediate pressures, they observed first shrinkage of the Ge-O bond lengths and then a jump to a metastable structure with a coordination number approaching five. The long-lived intermediate phase favors a transition from to low high pressure through two discrete jumps rather than a continuous transformation from fourfold to sixfold coordination. — MSL

Phys. Rev. Lett. 93, 115502 (2004).

Navigate This Article