Nature of the structural transformations in BO glass under high pressure

Brazhkin, V. V.*; Katayama, Yoshinori; Trachenko, K.*; Tsiok, O. B.*; Lyapin, A. G.*; Artacho, E.*; Dove, M.*; Ferlat, G.*; Inamura, Yasuhiro; Saito, Hiroyuki

We study polyamorphism of BO glass using X-ray diffraction up to 10 GPa in the 300-700 K temperature range, in situ volumetric measurements up to 9 GPa, and first-principles simulations. The glass undergoes two-stage transformations under pressure including a gradual increase of the first B-O (O-B) coordination numbers above 5 GPa. The fraction of boron atoms in the fourfold-coordinated state at P10 GPa is smaller than was assumed from inelastic X-ray scattering spectroscopy data, but is considerably larger than was previously suggested by the classical molecular dynamics simulations. The observed transformations under both compression and decompression are broad in hydrostatic conditions.