Spontaneous nucleation of cubic boron nitride single crystal by temperature gradient method under high pressure

Abstract

A single crystal of cubic boron nitride (cBN) was grown by spontaneous nucleation at high pressure and high temperatures of 5.5 GPa and 1500–1700°C for 20–80 h. The temperature gradient method was applied for the crystal growth using lithium boron nitride, barium boron nitride and their mixture as solvents. The morphology of grown crystals was strongly affected by the growth temperature and solvent. It can be seen that there was a limited P–T area, where facetted single crystals of good shape 1–3 mm in size could be obtained by spontaneous nucleation. The color of the grown crystals was affected by the solvent used. Amber-color crystals were obtained by using lithium boron nitride solvent, while colorless crystals were obtained by using barium boron nitride. Optical absorption, Raman spectroscopy, and chemical analysis of the grown crystals suggested that the color of the crystals was related to the amount of oxygen impurity in them.