Lithium Borates from the Glass to the Melt: A Temperature-Induced Structural Transformation Viewed from the Boron and Oxygen Atoms

Abstract

A multi-edge study of the local structure of lithium borate glasses and melts has been carried out using X-ray Raman scattering (XRS) as a function of temperature. Thanks to a wide range of compositions, from pure B 2 O 3 up to the metaborate composition, we are able to finely interpret in detail the modifications of the local environment of both the boron and oxygen atoms in terms of boron coordination number, formation of non-bridging oxygens (NBOs) and polymerization's degree of the borate framework as a function of temperature and composition. A temperature induced [4] B to [3] B conversion is observed above the glass transition temperature (T g ) from the glass to the melt from the triborate composition up to the metaborate composition. Two distinct melt structures are reported: a well polymerized borate network -with few NBOs -below the triborate composition, and a depolymerized borate network above the diborate composition with a rapid increase of the number of NBOs when Li 2 O is added. These two structurally distinct melts allow explaining the two dynamical regimes observed for lithium ion diffusion.

Liquid fragility maximum in lithium borate glass‐forming melts related to the local structure

“…the upper bound of 15%-8%, respectively). For a liquid with composition 70Li 2 O⋅30B 2 O 3 at 723 K, a value of N 4 = 5(10)% has recently been derived using inelastic X-ray scattering at the boron K-edge, 24 and this is also in good agreement with our results for lithium pyroborate. In the same study, the authors report 24 for lithium metaborate liquid at 1077 K, a value of N 4 = 12(9)%, which is also in good agreement with our previous data 9 for LiBO 2 liquid, which we have also shown to be consistent with various experimental studies on the lithium metaborate glass, and both classical and ab initio molecular dynamics modeling of the liquid.…”

Ion association in hydrothermal aqueous NaCl solutions: implications for the microscopic structure of supercritical water

“…A well-established analysis scheme of previous XRS studies consists of using either the peak intensity or the integrated intensity of spectral features to quantify the variation of spectral features with density and to assess the consistency of the calculations with the experiment 35,36,73,78,81,82 . Following this analysis scheme, we integrated the spectral features with the most significant changes, namely the pre-edge and the post-edge.…”

The dual role of bismuth in Li2O–Bi2O3–B2O3 glasses along the orthoborate join

“…Observing that the scattering at about 1460 cm −1 moves in tandem with the characteristic pyroborate features at 1435 (IR), 835 (Raman), and 1180 cm −1 (Raman and IR), the 1460 cm −1 shoulder is presumed to be associated with trigonal pyroborate species. One possibility that cannot be excluded is the presence of Li 6 B 4 O 9 type structural units described by Lelong et al 61,62 The Li 6 B 4 O 9 structure consists of two adjacent metaborate triangles forming a short four-member chain with pyroborate triangles at the ends. 62 The presence of this structure would be facilitated by the disproportionation of pyroborate species through the reaction 3B 2 O 5 4− ⇌ B 4 O 9 6− + 2BO 3 3− .…”