Boroxol ring dissolution in molten and glassy B2O3 by neutron and x-ray diffraction difference methods.

Area of Science:

• Materials Science
• Condensed Matter Physics
• Inorganic Chemistry

Background:

• Boron oxide (B2O3) is a key glass-forming material with a complex structure.
• Previous studies on B2O3 structure and thermal expansion have yielded conflicting results.
• Understanding the atomic-level structure is crucial for predicting material properties.

Purpose of the Study:

• To precisely measure the structure of B2O3 glass and liquid over a wide temperature range.
• To resolve the thermal expansion of the B-O bond.
• To identify and characterize the B-B interatomic interactions in B2O3.

Main Methods:

• Pulsed neutron diffraction was employed to study B2O3 from 14 K to 1500 K.
• High-energy X-ray diffraction data was utilized for comparison.
• Difference functions were calculated using neutron and X-ray scattering contrasts to isolate specific atomic pair correlations.

Main Results:

• Thermal expansion of the B-O bond was resolved, with a coefficient αBO = 4.1(3) ppm K⁻¹.
• A nearest-neighbor B-B peak was observed for the first time in the pair distribution function at rBB = 2.430(1) Å for glass.
• In the liquid phase, rBB increased to ~2.54 Å, suggesting changes in structural units like boroxol rings.

Conclusions:

• The study provides quantitative data on B2O3 thermal expansion, agreeing with prior X-ray diffraction results.
• The identification of the B-B peak offers direct evidence of inter-B2O3 interactions.
• Structural changes in liquid B2O3, particularly concerning boroxol ring fractions and bond angles, were elucidated.