高温高压下cBN单晶转变机理的密度泛函理论研究

DFT Theory Study of the Transition Mechanism of cBN Single Crystal under High Temperature and High Pressure

为研究Li_3N-hBN体系中cBN单晶的转变机理,本文采用基于密度泛函理论的赝势平面波方法和广义梯度近似法(GGA)系统计算了高温高压条件下hBN和cBN的低指数晶面的晶面能,分析了hBN和cBN各晶面之间的能量关系。结果表明:在1800K,5.5 GPa和2000 K,6.0 GPa下,hBN的(1010)晶面与cBN的(100)晶面的相对晶面能差分别为0.7%和1.2%,两组晶面的晶面能连续,即微观上电子密度连续。根据改进后的密度泛函理论(TFDC)可知,hBN能够向cBN直接转变。因此推断:在Li_3N-hBN体系中,以Li_3N为触媒,cBN单晶是由hBN直接转变而来。

The surface energy of the surface planes of the hexagonal boron nitride （ hBN） and cubic boron nitride （ cBN） was calculated to study the transition mechanism of cBN single crystal, using pseudopotentials plane wave method and the generalized gradient approximation （ GGA） based on density functional theory （ DFT） under high temperature and high pressure （HTHP）. It is found that the latticeplane of（1010）in hBN is consecutive with plane （100） of cBN, and relative difference of hBN（1010） and cBN （100） in surface energy is only 0.1% and 1 .2% under 1800 K ,5 . 5 GPa and 2000 K ,6 . 0 GPa, respectively. According to the TFDC theory, the direct transition of hBN into cBN can be induced.This indicates that cBN is most likely to be transformed by the hBN under high temperature and high pressure （HTHP） from the perspective of surface energy of hBN and cBN.