Removing Impurity of cBN Crystal Prepared at High Pressure and High Temperature

The black cubic boron nitride (cBN) single crystal is synthesized by using hBN-LiH and hBN-Li₃N−B as the raw materials at high temperature and high pressure (HTHP). The colors of the cBN crystal synthesized in an hBN-Li₃N−B system vary from transparent yellow, half-transparent and then opaque black with the increasing B content in the raw materials. It is worth noting that a trigonal shadow is presented at the center of the cBN crystal synthesized in the hBN-Li₃N-B system but can not be found in the hBN-LiH system. Analyzing the Raman spectrum, we find that the darkening and the trigonal shadow in the cBN crystal may be due to the presence of excess B atoms. The above-mentioned phenomenon can be determined by removing impurity capacity and growth environment of the cBN crystal.