Growth of boron suboxide crystals in the B–B₂O₃ system at high pressure and high temperature

B₆O crystal growth from the B–B₂O₃ system was investigated at 1700–2200 °C and 4.5–6.5 GPa by using two different sample assemblies. Single B₆O crystals over 100 μm in size have been synthesized at 5.5 GPa and 2100 °C. This makes it possible to study the properties of this interesting material. The factors affecting the B₆O crystal morphology, size, color, and growth process were discussed. The solubility of B₆O in B₂O₃ flux was estimated at 5.5 GPa and different temperatures. On the basis of the experimental results, we suggest two methods to grow large B₆O crystals.