XRD and micro-Raman study of structural transformations in (B2O3)_{1-x}(H2O)_x glasses and liquids
Liquid water and vitreous B$_2$O$_3$ are the endpoints of a continuous range of random networks in which hydrogen bonds gradually replace covalent bonds. Previous work has shown that glasses can be obtained by quenching in the range $x \le$ 0.50. We report the wide-angle x-ray scattering by the liquid phase in the composition range from $x$ = 0.38 to $x$ = 1.00 (pure water) at temperatures just above the liquidus. The first sharp diffraction peak (FSDP) remains at an approximately constant position in the range from $0 \le x \le 0.8$. Beyond this range, the position of the FSDP shifts linearly to higher angles. The relative concentration of the molecular species in the glasses and melts were measured with micro-Raman spectroscopy. Small molecular species are found for glasses and liquids with $x > 0.36$, determining the critical point at which the sample ceases to be a single macromolecule. Molecular water is present in liquids with $x > 0.62$.