Polyamorphism and Structural Transformation in Liquid B2O3 under Compression: Insight from Visualization of Molecular Dynamics Data

Abstract

Abstract: The structural order, polyamorphism and structural change of liquid B₂O₃ at 3000 K and in a 0-40 GPa pressure range are investigated by molecular dynamics simulation. Results show that the network structure of liquid B₂O₃ is formed from BO_x basic structural units (x=3, 4). At ambient pressure, most of basic structural units (coordination units) are BO₃ (over 99%). The BO₃ basic structural units are linked each to other via OB₂ linkages. At high pressure, the network structure of liquid B₂O₃ comprises of both BO₃ and BO₄ units linked each to other via OB₂ or OB₃ linkages. The bond angle and bond length distribution in BO_x units is not dependent of pressure. In other word, the topology structure of BO_x units in different models is identical. The bond angle distribution in OB₂ linkages depends strongly on pressure meanwhile the bond angle distribution in OB₃ linkages does not depend on pressure. With increasing pressure, liquid B₂O₃ transforms gradually from a BO₃- network structure (at low pressure) to BO₄- network structure (at high pressure). The distribution of BO_x in model is not uniform but tends to form the clusters of BO_x units. The clusters of BO₃ the form low density regions, conversely the clusters of BO₄ form the high density regions. The size of low and high density regions is strongly dependent of pressure.

Keywords:Polyamorphism, molecular dynamics simulation, B₂O₃, structure.