Ab Initio Study Of Crystal Structure And Electronic Structure For N-Diamond

The n-diamond powders can be synthesized by various processes, but the studying of n-diamond was tampered mainly due to the small amount of n-diamond samples and the tiny crystalline size (typically less than 100 nm) in many experiments. Thus, only transmission microscopy and electron diffraction were feasible for stru. rural analysis of n-diamond in those experiments. Recently, our group has synthiesized the n-diamond powders in large amount by the methods of catalysed carbon black in a high magnetic field, which established for studying its character. National research started on character of n-diamond just now and was unknown for the structure of n-diamond.After pyrogenation of carbon black and nanometer-sized iron catalyst at atmospheric pressure and a temperature of 1100℃, n-diamond nanometer-particles have been synthesized. The powder samples of n-diamond after arious aging-treatment times were investigated by x-ray diffraction (XRD). The XRD indicated that the n-diamond was a metastable phase and its crystal structure changed with the aging-treatment timer at room temperature. Based on the XRD analysis and the previous experimental results from TEM experiment, a "defective diamond" model with fractional occupation site was proposed to explain the time-dependent variations of the n-diamond crystal structure. The crystal model of n-diamond might be close to a face-central cubic (fcc) crystal with x=0, while the occupation number x=1 leads to a perfect diamond. The density function theory (DFT) computational cohesive energy further confirms the increase of stability with increasing occupancy number. Therefore, we suggest that n-diamond is indeed an intermediate state between the fcc structure and diamond structure. Based on the ab initio density functional theory, the electronic structure of the n-diamond was investigated by contrast with diamond and graphite. The results indicate that the n-diamond is a metallic form of carbon.