The defects of cBN single crystals were characterized by their optical absorption and etch-pit density. The crystals were synthesized by using temperature gradient method under high pressure. Compounds of alkali metal and/or alkali earth metal-boron nitride and metal of Ni-Al alloy were used as solvent for the crystal growth. Recovered crystals exhibited a variety of colours and crystalline natures, which were characterized by optical absorption and Raman spectroscopy. Chemical treatment was applied to the typically grown crystals so as to evaluate their etch-pit density. Colourless crystals obtained by using Ba-BN solvent system revealed superior properties showing high optical transmittance as well as lower etch-pit density of the order of 104/cm2.

Defect Characterization of cBN Single Crystals Grown under HP/HT. T.Taniguchi, K.Watanabe, S.Koizumi: Physica Status Solidi A, 2004, 201[11], 2573-7