The Crystallization of BN and the Synthesis of cBN at High Pressure and Temperature

The crystallization of amorphous, turbostratic and low crystalline degree hexagonal BN was found at high pressure and temperature and the conversion behavior of various BN with different crystallinity to cBN were studied. Results show that the synthesis of cBN is getting difficult as the crystallinity of starting BN material becomes worse (i.e. G.I value increase). When synthesizing cBN using hexagonal BN doped with B, we found that B can hinder the conversion to cBN. The existence of high nitrogen vacancies in low crystallinity BN may explain why it is difficult to transform to cBN. When BN crystallizes at high pressure and temperature, boron escapes which hinders the conversion of hBN to cBN.