Point defects in cubic boron nitride crystals

The results of a low-temperature study by high frequency (94 GHz) EPR on br own-to-dark colored single crystals selected from cBN crystalline powders p repared by the HPHT technique with boron excess, are presented. Previous in vestigations by low frequency (9.4 GHz) EPR spectroscopy on such dark polyc rystalline c-BN powders resulted in the identification of two paramagnetic species D1 and D2 associated with the brown-to-dark coloration, the spectru m of the latter one being observed only above 100 K. The present research i dentifies the D1 species, studied by EPR at low temperatures, as consisting mainly from anisotropic paramagnetic centers with electron spin S = 1/2, l ocal symmetry axis along one of the crystal [111] axes and principal g valu es g(parallel to) = 2.0032 +/- 0.0009 and g(perpendicular to) = 2.0094 +/- 0.0005 at T = 10 K. (C) 2001 Elsevier Science B.V. All rights reserved.