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

  • Sheng-Nian Luo , Oliver Tschauner EMAIL logo , Paul D. Asimow and Thomas J. Ahrens
Published/Copyright: March 28, 2015
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Abstract

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.

Received: 2003-8-5
Accepted: 2003-11-17
Published Online: 2015-3-28
Published in Print: 2004-2-1

© 2015 by Walter de Gruyter Berlin/Boston

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