Crystallization and Phase Relations of Boron Trioxide at High Pressures

Crystalline B 2 O 3 was readily obtained from the glassy phase at high pressures and temperatures. Single crystals 0.3 mm. in dimension of both α‐B 2 O 2 (ordinary hexagonal) and β ‐B 2 O 3 (dense monoclinic) were prepared. The difference in the density of the two forms was about 20%. Crystals of β ‐B 2 O 3 were only slowly attacked by H 2 O and dilute HF. At atmospheric pressure, transitions between the α‐ , β ‐, and liquid phases were extremely sluggish. A tentative phase diagram was constructed up to 1100°C. and 90,000 atmospheres, the probable melting curve being calculated by the use of the Simon melting equation.