Report

Observation of the transition state for pressure-induced BO3→ BO4 conversion in glass

Science  29 Aug 2014:
Vol. 345, Issue 6200, pp. 1027-1029
DOI: 10.1126/science.1256224

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Catching changing boron coordination

Laboratory glassware and kitchen cookware alike are made of glass that contains different cations, including boron, sodium, and aluminum. Properties of glass depend on the number and location of oxygen atoms surrounding each cation. Edwards et al. combine nuclear magnetic resonance measurements with theoretical calculations to understand structural transformations in borosilicate glass (see the Perspective by Youngman). Boron atoms in planar threefold coordination move out of plane with increasing pressure to form trigonal pyramids. Identification of this type of transition state connects structural evolution with stress-induced processes in amorphous materials. In borosilicate glass, the transition leads to the formation of tetrahedral fourfold-coordinated boron that tunes glass properties for use in numerous applications.

Science, this issue p. 1027; see also p. 998

Abstract

A fundamental mechanistic understanding of the pressure- and/or temperature-induced facile transformation of the coordination environment of boron is important for changing the physical properties of glass. We have used in situ high-pressure (up to 2 gigapascals) boron-11 solid-state nuclear magnetic resonance spectroscopy in combination with ab initio calculations to investigate the nature of the transition state for the pressure-induced BO3→ BO4 conversion in a borosilicate glass at ambient temperature. The results indicate an anisotropic elastic deformation of the BO3 planar triangle, under isotropic stress, into a trigonal pyramid that likely serves as a precursor for the subsequent formation of a BO4 tetrahedron.

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