First-Principles Studies on the Structure and B–O Coordination of B₂O₃ Glass at High Pressure

Abstract

The structures of amorphous materials at extreme pressures can be very different from those of their crystalline counterparts. Recent nonresonant inelastic scattering experiments on B 2 O 3 glass performed up to ∼120 GPa have suggested that B− O coordination numbers higher than 4 were presented. In this study, B 2 O 3 glass structures up to 350 GPa were generated from first-principles molecular dynamics (FPMD) calculations. X-ray and neutron diffraction patterns, B K-edge X-ray absorption spectra, and 11 B NMR spectra were computed and compared to experiments. The nature of the B−O interactions was characterized by Bader's quantum theory of atoms in molecules (QTAIM) analysis and electron localization function (ELF). The theoretical results found that 5-and 6-coordinated B exists at high pressure. However, not all of the B and O contacts are covalently bonded. Instead, both BO 5 and BO 6 groups consisted of 4 short B−O covalent bonds with weaker B−O interactions with the other O atoms. Structure prediction calculations were performed at a similar pressure range to assess whether 6-coordinated B−O can exist in crystalline B 2 O 3 . No genuine 6-coordinated B was found. The high B−O coordination number in the glass is simply due to compaction at high pressure.