Polyamorphism and Structural Transformation in Liquid B2O3 under Compression: Insight from Visualization of Molecular Dynamics Data
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 BOx 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 BOx units is not dependent of pressure. In
other word, the topology structure of BOx 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 BOx in model is not uniform but tends to form the clusters of BOx
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.