Liquid B₂O₃up 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 (>~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 αBO = 3.7(2) × 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.

Rare‐earth titanate melt structure and glass formation

“…The pyrometer temperature was also corrected for reflection losses from a CaF 2 window and lens that were in the optical path. The diffraction data reduction and definitions of the scattering functions used are given elsewhere . The measured structure factors, S ( Q ), represented as functions of Q = (4 π sin ϑ )/ λ , with 2 ϑ the scattering angle, and λ = 0.12370 Å the X‐ray wavelength, were Fourier transformed with Q max = 20 Å −1 , without modification (window) function.…”

Local structural variation with oxygen fugacity in Fe2SiO4+ fayalitic iron silicate melts

“…The analysis, particularly of the diffraction data, requires knowledge of both the melt density and composition (Alderman et al, 2015;Alderman et al, 2014;Fischer et al, 2006;Keen, 2001). Liquid mass densities were estimated from measurements (Shiraishi et al, 1978) at 1573 K and 1673 K by linear interpolation or extrapolation using ρ = 3.373 -0.00028(T -1573) in g cm -3 and K which yields densities about 1% higher than some more recent measurements (Thomas et al, 2012).…”

“…The Fourier transforms (defined in (Alderman et al, 2015;Alderman et al, 2014)) of the diffraction data are presented in Fig. 5a and 5b in the form of D(r) and T(r).…”

“…5b. Fitted peak shapes consisted of Gaussian distributions convolved with the Fourier transforms of both the x-ray pair weighting function W ij (Q) and the modification function, M(Q), to match the experimental data (Alderman et al, 2015). For the measurements made at 100 keV, which have lower resolution, the Si-O peak was simulated (rather than fitted) with bond-length r SiO = 1.64 Å, root-mean-square deviation 〈u SiO 2 〉 1/2 = 0.095 Å, and coordination number n SiO = 4, estimated from measurements at similar temperatures on pure liquid SiO 2 (Skinner et al, 2013b).…”

Determining the Structure of Stable and Supercooled Liquids by High Energy X-Ray Diffraction

“…Experiments performed for example at the beamlines 11-ID-C and 6-ID-D at the APS have demonstrated that high energy X-ray diffraction measurements are an extremely effective in studying the liquid and amorphous states. A range of materials have been studied including silicate [6] and aluminate liquids [7], TiO2 [8], borates [9,10] and, recently molten uranium oxide [11,12].…”