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By developing new strategies, cubic boron nitride crystals (cBN) were selectively synthesized by a hydrothermal method using H 3 BO 3 , NH 3 $H 2 O and N 2 H 4 $H 2 O as the reactants. The experimental results indicated that both the relative content and crystalline perfection of cBN were improved by increasing the reaction temperature. Furthermore, we developed two new strategies, i.e., pressurizing the reaction solution (with nitrogen) and quickly cooling down thereafter. As a result, cBN content and its crystalline perfection were also obviously improved. In addition, NaCl and NaF were found to possess the induction effect of promoting cBN formation, and the effect of NaF is much stronger than that of NaCl. In conclusion, by optimizing the preparation parameters and applying these new strategies, nearly pure cBN with quite high crystallinity has been prepared from hydrothermal solutions.

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