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.