Structural transformations of boron trioxide under high pressure and high temperature

A systematic study of boron trioxide under high pressure and high temperature (HPHT) was conducted using a Chinese multi-anvil high-pressure apparatus (CHPA). The HPHT phase diagram was determined using X-ray diffraction measurements. Under high pressure (3.6–5.5?GPa) and low temperature (below 450?°C), the boron trioxide grains were reduced to the nanometer size and the hardness reaches to 13.9?GPa (5.5?GPa and 450?°C). The boroxol rings were produced only in the glass phase that was transformed from the α-B₂O₃ phase under HPHT. And the formation mechanism of boroxol rings was discussed according to Raman spectrum and crystal structure of α-B₂O₃ and β-B₂O₃.