超高温高压下石墨向金刚石直接转变的理论研究

First-principles Calculation of the Lattice Parameters of Graphite at High Temperature and High Pressure

根据固体和分子经验电子理论（EET理论），分别计算了静压法和爆炸法合成金刚石过程中石墨和金刚石的价电子结构，获得了超高温高压下石墨和金刚石12组不同组合晶面间的价电子密度，结果表明，采用静压法合成金刚石．石墨／金刚石晶面的电子密度差均大于10％，说明其晶面的价电子结构差异太大，不能诱发石墨向金刚石的直接转变。而采用爆炸法合成金刚石，石墨结构理论键距和实验键距差是0．1073nm，明显大于稳定的价电子结构键距差的最大值（0．005nm），因此，爆炸法条件下，石墨的价电子结构不稳定，主要因为超高温高压下，石墨先分解出亚稳相后再转变成金刚石结构。

The lattice parameters of graphite at high temperature and high pressure were computed using ab initio density-functional theory with the generalized gradient approximation and the local dens approximation, respectively. Good agreement was achieved between the calculated and experimen lty tal results in lattice parameters a, with the maximum relative differences about 1.2%. Meanwhile, the calculated lattice parameters c were also reasonably consistent with the experimental results with the maximum relative difference about 8.9%. It was also found that both a and c/a increased slowly with increasing temperature, but decreased dramatically with of pressure on the lattice parameters. increasing pressure, indicating the greater impact