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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 (LiaBN2).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.