The near-Surface Region of Cubic Boron Nitride Single Crystal from the Li₃N-hBN System

Cubic boron nitride single crystals are synthesized with lithium nitride as a catalyst under high pressure and high temperature. The main phases in the near-surface region, which around the single crystal are determined as a mixture of hexagonal boron nitride (hBN), cubic boron nitride (cBN) and lithium boron nitride (Li₃BN₂). High resolution transmission electron microscopy examinations show that there exist lots of nanometer-sized cubic boron nitride nuclei in this region. The interface phase structures of cubic boron nitride crystal and its near-surface region are investigated by means of transmission electron microscopy. The growth mechanism of cubic boron nitride crystal is analyzed briefly. It is supposed that Li₃BN₂ impels the direct conversion of hBN to cBN as a real catalyst, and cBN is homogeneously nucleated in the molten state under high pressure and high temperature.