Observation of the transition state for pressure-induced BO ₃ → BO ₄ conversion in glass

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.

Short-range and Medium-range Structural Order in CaO–SiO₂–TiO₂–B₂O₃ Glasses

“…For example, Stebbins et al found a conversion of BO 3 trigonal to BO 4 tetrahedral with increasing temperature. 11) Recently, Edwards et al 12) discovered the dynamic process of the BO 3 →BO 4 conversion with increasing pressure using a high pressure 11 B solid state Nuclear Magnetic Resonance (NMR) spectroscopy. There appears a deformation of the BO 3 planar triangle into trigonal pyramid, which serves as a precursor for the formation of BO 4 tetrahedral.…”

Interconversion between Planar-Triangle, Trigonal-Pyramid and Tetrahedral Configurations of Boron (B(OH)<sub>3</sub> -B(OH)<sub>4</sub><sup>-</sup> ), Carbon (CH<sub>3</sub><sup>+</sup> -CH<sub>3</sub>X) and for the Group 15 Elements as Nitrogen (NH<sub>3</sub>-NH<sub>4</sub><sup

“…In the report of Edwards et al [11] it was established that the out-of-plane displacement of the boron atom is consistent with the in situ high-pressure NMR spectra. This mode of deformation for the 11 Bδ iso value is given in Figure 2.…”

“…This mode of deformation for the 11 Bδ iso value is given in Figure 2. Out-of-plane displacement of boron in B(OH) 3 following the characteristics of the Van't Hoff (vtH) modelling under subsequent formation of a tetrahedral configuration.…”

“…The latter line has relevance because it demonstrates clearly the asymptotic character based on the maximum value of the out-of-plane orientation. A linear plot has been shown for the relation between 11 Bδ iso and the variation in bond length of one of the B-O bonds in the planar B(OH) 3 . This representation conflicts with the absence of significant changes in the quadrupole parameters.…”

“…As mentioned before, this model has been used to describe the pressure-induced conversion of a BO 3 triangle in planar B(OH) 3 into a trigonal pyramid [11]. The latter structure may be considered as transition state in the formation of a tetrahedral configuration effectuated by local coordination environments via atomic oxygen sites …”