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Structural transformations and anomalous viscosity in the B2O3 melt under high pressure
V V Brazhkin1, I Farnan, Ken-ichi Funakoshi
1Institute for High Pressure Physics RAS, 142190 Troitsk Moscow region, Russia. brazhkin@hppi.troitsk.ru
Physical Review Letters
|September 28, 2010
Summary
High pressure dramatically alters liquid boron trioxide (B2O3) structure and viscosity. Boroxol rings disappear, replaced by four-coordinated boron, causing a four-order-of-magnitude viscosity drop.
Area of Science:
- Materials Science
- Geophysics
- Physical Chemistry
Background:
- Liquid boron trioxide (B2O3) is a model oxide melt known for its exceptionally high viscosity.
- Understanding its behavior under pressure is crucial for materials science and geophysics.
Purpose of the Study:
- To investigate the structural transformations and viscosity changes in liquid B2O3 under high pressure.
- To elucidate the pressure-induced changes in the coordination of boron atoms.
Main Methods:
- In situ X-ray diffraction and viscosity measurements up to 8 GPa.
- 11B solid-state NMR spectroscopy on quenched B2O3 glasses.
Main Results:
- The fraction of boroxol rings in liquid B2O3 decreases significantly with increasing pressure.
- Four-coordinated boron states emerge sharply around 4.5 GPa, reaching 40%-45% at 8 GPa.
- Viscosity drops by four orders of magnitude up to 5.5 GPa, then plateaus.
Conclusions:
- High pressure induces significant structural changes in liquid B2O3, including a transition from three- to four-coordinated boron.
- These structural changes are directly responsible for the dramatic decrease in viscosity observed under pressure.
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