摘要
本文在hBN-L i3N体系中添加不同含量的单质硼(B),研究了cBN晶体在富B条件下的生长特性。结果表明,B进入晶体的位置具有明显的区域选择性。B以占据N(111)面内N空位的方式进入晶体,并与原有的N原子一起形成一个B原子和N原子的(111)面。随着B进入量的增加,越来越多的B原子取代N空位,B和N原子的混合面与邻近的B(111)面叠加,在晶体的中心部位形成颜色较深的三角形阴影并逐步扩展,最后,使晶体完全变成黑色。由于B占据N空位造成原来N的(111)面上有大量硼原子存在,使得晶体沿<111>方向生长困难而有利于沿<100>方向生长,从而形成了八面体或类球形晶体。同时,由于加入的B与部分L i3N发生化学反应也可生成cBN,因此,体系中cBN晶体的形成受两种机制控制:一种为溶解析出过程,另一种为化学反应过程。cBN的产率随着B添加量的增加而降低的实验结果表明,溶解析出过程占主导地位。
In this paper, growth characters of cBN crystal in hBN- Li3N system with different contents of B additive were investigated under high pressure and high temperature. The results show that boron atoms entering cBN crystal had distinct location character. B atoms occupy N vacancies in the （ 111 ） plane and therefore leads to forming a new plane made of B and N atoms. With B additive increasing, more N vacancies are substituted. The new B-N （ 111 ） plane and its neighboring B （ 111 ） plane overlapping with each other resulted in forming dark triangle shadow in （ 111 ） plane of cBN crystal. The triangle extended through to the whole cBN crystal, which changed the color of cBN crystal into black. Owing to excessive B locating at N （ 111 ） planes, the growth of cBN crystals along 〈 111 〉 direction became difficult while the growth along 〈 100 〉 direction was favorable. So the morphology of the obtained cBN crystals changed from thick plank into near perfect octahedron or sphere-like morphology. At the same time, cBN could be also obtained by the chemical reaction between Li3 N and B, so the formation of cBN crystal in this B-rich system could be controlled by two mechanisms： dissolve-recrystallization and chemical reaction process. The experimental results show cBN nucleation decreases with B additive increases. This indicates that the dissolve- recrystallization is dominant process in the B-rich system, if Li3N is excessive.
出处
《人工晶体学报》
EI
CAS
CSCD
北大核心
2006年第6期1268-1271,共4页
Journal of Synthetic Crystals
