Synthesis of high-quality octahedral cBN crystals with large size using lithium metal as a catalyst

• We synthesizedhigh-quality octahedral cBN crystals with large size.
• The octahedral cBN crystals exhibit black color.
• Maximum size and average compressive strength are 400 μm and 47.5 N, respectively.

High-quality octahedral cubic boron nitride (cBN) crystals with large size and black color have been synthesized using lithium metal as a catalyst under high pressure and high temperature. The maximum size and average compressive strength of the octahedral cBN are respectively 400 μm and 47.5 N, which are larger than those reported. The morphology and size of the crystals depend closely on pressure and temperature, and a P–T diagram for the formation of the cBN crystals is obtained. The formation mechanism of the octahedral cBN crystals is proposed in terms of the Raman spectra and X-ray diffraction patterns.