Experiments And First Principls Study Of Crystal Structure For New Diamond

As a novel kind of carbon allotropes, the new diamond(n-diamond) has aroused wide attention due to its great research value and potential application. So far, many methods of experimental preparation for n-diamond have been reported, but the yield and purity of the n-diamond prepared by these methods are very low. This seriously impedes the development of new diamond. In addition, many theoretical models have been also proposed to explain the structure of n-diamond, however, most of these models are dynamically unstable, as for the stable model, the simulated x-ray diffraction is very different from that of experimental results. In other words, the structure of n-diamond is still a mystery up to now.To address the above problems, the n-diamond has been studied both in experimental preparation and theoretical prediction of its structure in this paper. The experiment was based on the method of nano-sized Fe catalyzed carbon black. The carbon black was adopted as the carbon source and the nano-sized Fe was used as catalyst in this experiment. The n-diamond was successfully synthesized in argon atmosphere at high temperature, and it had been carried on the purification. The first-principles prediction was proceed by the experimental results that n-diamond is a three dimensional(3D) metallic carbon.The mixed powder for experiment was prepared by carbon black as carbon source and nano-sized Fe as catalyst, and the molar ratio of carbon black and nano-sized Fe is 4:1. The mixed powder was heated in high-temperature tube furnace, and the mixed powder was kept at 1100℃ for an hour. After the mixed powder cooled, the XRD results indicated that n-diamond was successfully synthesized in the powder material under our experimental conditions. It was found that n-diamond will be decomposed under acidiccondition, the magnet was used to remove the catalyst nano-sized Fe in the powder material containing n-diamond. Through the above experimental preparation and purification, massive high purity of n-diamond powder can be produced, which will be very helpful for the research work of n-diamond.By the means of first-principles calculations, two kinds of 3D metallic carbon have been proposed, and they are the polymerized fullerene model(sc-C96) and the distorted sp3 hybrid carbon model(Tri-C9), respectively. The calculated results showed that two models are the metastable and metallic phase. The sc-C96 is a kind of 3D topological nodal line semimetallic carbon, and it can be easily obtained by the polymerizing C96 fullerene molecules. But it is a pity that the simulated XRD results revealed that the sc-C96 is not the structure of n-diamond. Tri-C9 is a kind of sp3 hybrid metallic carbon, its density is closed to that of diamond, and its vicker hardness is about 35 GPa. Tri-C9 may be obtained by compressing graphite under the pressure of 70 GPa. The XRD simulation results demonstrated that Tri-C9 will be very helpful to determine the crystal structure of n-diamond.