Molecular dynamics studies of vitreous boron oxide

Several structural investigations using diffraction techniques, Raman spectroscopy, nuclear magnetic resonance (NMR) and nuclear quadrupole resonance (NQR) have supported the idea that the structure of vitreous B2O3 (v-B2O3) is built up predominantly by planar B3O6 rings. Most Molecular Dynamics (MD) studies can be better understood by a continuous random network of BO3. In this work the structure of v-B2O3 has been investigated by MD simulations. The magnitude of the differences in model density samples is studied as a function of the ratio of structural units (B3O6 versus BO3). The difference in this ratio in generated structures was obtained by two cooling cycles: Cycle I is simulating a quenched structure while the Cycle II intents to reproduce a slowly cooled structure. It is shown that for structures containing several hundred atoms MD simulations give a considerable variation for the ratio of building units. The computed density for the obtained structures could not reach experimental density values for either of the cooling cycles. The number of boron atoms in boroxol rings is higher in the structures generated with slow cooling but is less than the predicted one of 80%.