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Liquid B2O3 up to 1700 K: x-ray diffraction and boroxol ring dissolution

Abstract : Using high energy x-ray diffraction, the structure factors of glassy and molten B2O3 were measured with high signal-to-noise, up to a temperature of T = 1710(20) K. The observed systematic changes with T are shown to be consistent with the dissolution of hexagonal [B3O6] boroxol rings, which are abundant in the glass, whilst the high-T (greater than or similar to 1500 K) liquid can be more closely described as a random network structure based on [BO3] triangular building blocks. We therefore argue that diffraction data are in fact qualitatively sensitive to the presence of small rings, and support the existence of a continuous structural transition in molten B2O3, for which the temperature evolution of the 808 cm(-1) Raman scattering band (boroxol breathing mode) has long stood as the most emphatic evidence. Our conclusions are supported by both first-principles and polarizable ion model molecular dynamics simulations which are capable of giving good account of the experimental data, so long as steps are taken to ensure a ring fraction similar to that expected from Raman spectroscopy. The mean thermal expansion of the B-O bond has been measured directly to be alpha(BO) = 3.7(2) x 10(-6) K-1, which accounts for a few percent of the bulk expansion just above the glass transition temperature, but accounts for greater than one third of the bulk expansion at temperatures in excess of 1673 K.
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Alderman et al. - 2015 - Liqui...
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O. L. G. Alderman, G. Ferlat, A. Baroni, M. Salanne, M. Micoulaut, et al.. Liquid B2O3 up to 1700 K: x-ray diffraction and boroxol ring dissolution. Journal of Physics: Condensed Matter, IOP Publishing, 2015, 27 (45), pp.455104. ⟨10.1088/0953-8984/27/45/455104⟩. ⟨hal-01502196⟩



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