Growth mechanism of cubic BN using Li3BN2 solvent under high pressure

• Growth pressure and temperature region of cubic BN was determined.
• Li3BN2 solvent was used as catalytic solvent.
• Meta-stable hexagonal BN phase was grown
• Lower pressure region, rate of nucleation of cubic BN was very slow.

The pressure and temperature region of the cubic BN precipitation was studied using Li3BN2 as synthetic solvent over the pressure and temperature range from 3.5 to 6 GPa and 1100 to 1800 °C for a duration of 0.3–11 h. The pressure and temperature region of cubic BN formation in the BN-Li3BN2 was bounded by lowest temperature line and highest temperature line of cubic BN formation at constant pressure value. We determined these lines as P(GPa) = [T(°C)/30] − 37 for the lowest temperature line and P(GPa) = [T(°C)/465] + 0.79 for the highest temperature boundary between cubic and hexagonal BN. The recovered samples reacted at pressure lower than about 5 GPa were mixture of re-crystallized hexagonal BN and cubic BN crystals. Meta-stable hexagonal BN grew rapidly in the cubic BN stable pressure and temperature region and cubic BN was grown slowly in the meta-stable hexagonal BN matrix.