高温高压下Fe-Ni-C系合成金刚石单晶的机理研究（上）

从三个方面综合介绍了本课题组近几年来采用Fe-Ni-C系在高温高压下合成优质金刚石单晶的研究成果：1）采用单质金属铁、镍粉和石墨粉以及粉末冶金方法制备出新型铁基触媒,利用六面顶压机合成了高品位的金刚石单晶;2）采用现代分析测试方法对金刚石单晶外的金属包覆膜物相结构进行了系统表征和分析;3）基于固体与分子经验电子理论（EET理论）和托马斯-费米-狄拉克-程开甲理论（TFDC理论）对金刚石合成过程中相关物相（金刚石、石墨、Fe3C（（Fe,Ni）3C）和γ-（Fe,Ni）等）的价电子结构进行了计算和论证。实验分析与理论研究结果表明,单质金属粉辅以粉末冶金方法同样可以实现高品位金刚石单晶的合成;金属包覆膜中存在大量的Fe3C、（Fe,Ni）3C类型的金属碳化物和γ-（Fe,Ni）型金属中间相,且γ-（Fe,Ni）与金属碳化物的对应晶面之间存在相互平行的位向关系;金刚石与石墨主要晶面间的平均共价电子密度在一级近似条件下均不连续,而Fe3C与金刚石或Fe3C与γ-（Fe,Ni）之间存在界面电子密度连续性,因此证明Fe3C/金刚石界面能够满足金刚石生长的边界条件。研究结果表明,金刚石单晶生长的碳源并非直接来源于石墨,而来源于在金属中间相的催化作用下,由金属碳化物过渡相中脱溶出的、具有类SP3杂化态的C-C原子团,因此从实验和理论上进一步支持了金刚石合成的＂溶剂-催化＂理论。

Mechanism of synthesizing diamond single crystal from Fe-Ni-C system under high-temperature and high-pressure

The important research results made by our research team in the past few years are introduced in this paper.They are composed of three parts： 1） yielding high-quality diamond single crystal with iron-based catalyst made by powder metallurgical method,using pure form of iron and nickel as main raw materials;2） general characterization and analysis of microstructure of metallic film surrounding diamond crystal by means of modern testing technology;3） calculation and analysis of valence electron structure of related phase（including diamond,graphite,Fe3C（（Fe,Ni）3C）,γ-（Fe,Ni） and so on） involved in the process of diamond synthesis,based on the empirical electron theory of solid and molecules（EET） and the improved Thomas-Fermi-Dirac theory by Cheng（TFDC）.The results of experiments indicate that high-quality diamond single crystal can be obtained with the iron-based catalysts made by powder metallurgical method.There are large number of metallic carbides and transition phase just like γ-（Fe,Ni） in the metallic film.In addition,some crystal planes of γ-（Fe,Ni） have the parallel orient relationship with those of some metallic carbides.The results of calculation show that the valence electron densities of common planes in graphite were not continuous with those of planes in diamond at the first order of approximation.On the contrary,the continuous relationship of valence electron densities appears on the interface of Fe3C and diamond as well as that of Fe3C and γ-（Fe,Ni）.It means that the boundary condition of diamond growth can be satisfied on the interface of Fe3C and diamond.All the results suggest that the direct carbon source of diamond growth is not graphite.The carbon atoms groups possess SP3 structure,which decompose from metallic carbides,deposit on the diamond nucleus surface and make it grow.The real catalyst is the metallic transition phase i.e.γ-（Fe,Ni）.Our research results agree with the solvent-catalyst theory.