On February 10, this reporter learned from Jilin University that the team of Prof. Liu Bingbing and Prof. Yao Mingguang from the university, together with Prof. Zhu Shengcai from Sun Yat-sen University, discovered a new pathway for the formation of hexagonal diamond from graphite via post-graphite phase under high temperature and high pressure, and synthesized for the first time a high-quality, nearly pure hexagonal diamond block material, which is found to have a higher hardness than that of cubic diamond and a good thermal stability. The related research results were published in the international academic journal Nature Materials.
Diamond, or diamond, has the reputation of “industrial teeth”. As early as 1967, American scientists in a meteorite crater found a rare “super diamond”, because it has a hexagonal crystal structure, symbiosis in the meteorite and more hard and attention. For half a century, synthesizing pure-phase hexagonal diamonds has been a long-standing scientific challenge.
The research team proposed a new mechanism for the transformation of graphite to cubic diamond, and found that the formation of the high-pressure phase structure of sp3 carbon is an important factor in the study of the effect of shear on the structural changes of graphite under high pressure. The related study inspired the team that the high-pressure phase structure is likely to be the key when exploring the synthesis of hexagonal diamond.
Considering the formation of meteorite diamonds, there are not only ultrahigh pressure but also high temperature conditions, the team designed high temperature and high pressure experiments for this purpose, and utilized the laser heating diamond to top anvil technology to study the change rule of the structure of graphite in the ultrahigh pressure and high temperature of 50 GPa in situ, and found that graphite in the high-pressure interval will form the “post-graphite phase” high-pressure structure, and then the graphite phase structure will be formed. Hexagonal diamond was successfully obtained by localized heating.
The research team found that hexagonal diamond has excellent physical properties, with a hardness exceeding 40% of natural diamond, and its thermal stability under vacuum environment can reach 1100℃, which is better than that of nanodiamond at 900℃. The team further combined with large-scale molecular dynamics theoretical simulations to reveal the key role of graphite layer stacking conformation in the formation of hexagonal diamond structure, confirming a brand new pathway for graphite to form hexagonal diamond via post-graphite phase.
According to the researchers, the results not only provide an effective way to synthesize pure-phase hexagonal diamond, giving strong evidence for its independent existence, but also add a new member with more excellent performance to superhard materials and new carbon materials, and provide a possible breakthrough in the application limitations of cubic diamond. The results are of great significance to the in-depth understanding of the specific origin of diamonds in meteorites and major geological events.
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