Synthesis of boron suboxide from boron and boric acid under mild pressure and temperature conditions

Graphical abstract: Well-crystallized and icosahedral B6O crystals were prepared by reacting boron and boric acid at milder reaction conditions (1 GPa and 1300 oC for 2 h) as compared to previous work.. Research highlights: → Well-crystallized icosahedral B6O was synthesized by reacting boric acid and boron. → The synthesis conditions (1 GPa and 1300 oC for 2 h) are milder in comparison with previous work. → The more practical synthesis method may make B6O as a potential substitute for diamond in industry. -- Abstract: Boron suboxide (B6O) was synthesized by reacting boron and boric acid (H3BO3) at pressures between 1 and 10 GPa, and at temperatures between 1300 and 1400 oC. The B6O samples prepared were icosahedral with diameters ranging from 20 to 300 nm. Well-crystallized and icosahedral crystals with an average size of ∼100 nm can be obtained at milder reaction conditions (1 GPa and 1300 oC for 2 h) as compared to previous work. The bulk B6O sample was stable in air at 600 oC and then slowly oxidized up to 1000 oC. The relatively mild synthetic conditions developed in this study provide a more practical synthesis of B6O, which may potentially be used as a substitute for diamond in industry as a new superhard material.