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American Mineralogist; February 2004; v. 89; no. 2-3; p. 455-461
© 2004 Mineralogical Society of America
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Letter

A new dense silica polymorph: A possible link between tetrahedrally and octahedrally coordinated silica

Sheng-Nian Luo1,4, Oliver Tschauner1,2,*, Paul D. Asimow3 and Thomas J. Ahrens1

1 Lindhurst Laboratory of Experimental Geophysics, Seismological Laboratory, California Institute of Technology, Pasadena, California 91125, U.S.A.
2 High Pressure Science and Engineering Center and Department of Physics, University of Nevada, Las Vegas, Nevada 89154-4002, U.S.A.
3 Division of Geological & Planetary Sciences, California Institute of Technology, Pasadena, California 91125, U.S.A.
4 Plasma Physics (P-24) and Earth and Environmental Sciences (EES-11), Los Alamos National Laboratory, Los Alamos, New Mexico 87545, U.S.A.

Correspondence: * E-mail: olivert{at}physics.unlv.edu

We present the discovery of a novel dense silica polymorph retrieved from shock-wave and diamond-anvil cell experiments. This polymorph is the first observed silicate composed of face-sharing polyhedra and it has a density similar to stishovite. Sterical constraints on the bond angles induce an intrinsic disorder of Si positions, such that the Si-coordination is transitional between four-and sixfold. The structure provides a mechanism for this coordination change in silica and other silicates at high temperature that is fundamentally different from mechanisms at 300 K. The new polymorph also illustrates how the face-sharing polyhedra, naturally occurring along previously proposed compression mechanisms for dense silicate melts, can be constructed without inferring unphysically small bond angles.




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O. Tschauner, S.-N. Luo, P. D. Asimow, and T. J. Ahrens
Recovery of stishovite-structure at ambient conditions out of shock-generated amorphous silica
American Mineralogist, November 1, 2006; 91(11-12): 1857 - 1862.
[Abstract] [Full Text] [PDF]


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