The influence of the h-BN morphology and structure on the c-BN growth

The morphology and structure of hexagonal graphitic BN (h-BN) powders with graphitization indices GI <5, used as precursors for the synthesis of cubic BN (c-BN) crystals, has been investigated by transmission electron microsc opy in diffraction contrast and high resolution. We show that besides the G I, which is a general parameter for controlling the structural quality of h -EN ponders, some other microstructural features strongly influence the syn thesis of c-BN. In our opinion, the high reactivity of some h-BN powders re sults from the presence of some nucleation centers for c-BN, observed at th e edges of the h-BN particles. They are formed by a rearrangement of the gr aphitic (0002) planes by bending back, joining in pairs and forming locally nanoarches (half nanotubes). In these particular places, the nature of bon ding locally turns towards sp(3), as in the case of c-BN, (C) 2001 Elsevier Science B.V. All rights reserved.