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美国劳伦斯利弗莫尔国家实验室A. Lazicki揭示了金刚石压缩到2TPa后的亚稳性。相关研究成果于2021年1月27日发表在国际知名学术期刊《自然》。

碳碳是宇宙中第四大元素，对所有已知生命都是必不可少的。在地球上，碳可以以许多不同的同素异形体的存在，包括石墨、金刚石和富勒烯，而且长期以来一直预测，在压力大于地球核心的压力下，甚至可以存在更多的结构。

据预测，在多个TPa区间存在多种相，这对于精确模拟富含碳的外行星的内部非常重要。通过使用激光脉冲将固体碳压缩到2TPa（2000万个大气压；是地球压力的五倍以上），并同时测量纳秒持续时间的X射线衍射，发现固体碳保留了金刚石结构，远远超出其预期的稳定性。

研究结果表明，在巨大的压力下，金刚石仍然存在四面体分子轨道键，导致了很大的能量势垒，阻碍了向更稳定的高压同素异形体的转化，正如亚稳金刚石的石墨在大气下形成是受到运动阻碍一样。

该项工作使在任何材料上记录X射线衍射的最高压力几乎翻倍。

附：英文原文

Title: Metastability of diamond ramp-compressed to 2 terapascals

Author: A. Lazicki, D. McGonegle, J. R. Rygg, D. G. Braun, D. C. Swift, M. G. Gorman, R. F. Smith, P. G. Heighway, A. Higginbotham, M. J. Suggit, D. E. Fratanduono, F. Coppari, C. E. Wehrenberg, R. G. Kraus, D. Erskine, J. V. Bernier, J. M. McNaney, R. E. Rudd, G. W. Collins, J. H. Eggert, J. S. Wark

Issue&Volume: 2021-01-27

Abstract: Carbon is the fourth-most prevalent element in the Universe and essential for all known life. In the elemental form it is found in multiple allotropes, including graphite, diamond and fullerenes, and it has long been predicted that even more structures can exist at pressures greater than those at Earth’s core1,2,3. Several phases have been predicted to exist in the multi-terapascal regime, which is important for accurate modelling of the interiors of carbon-rich exoplanets4,5. By compressing solid carbon to 2 terapascals (20 million atmospheres; more than five times the pressure at Earth’s core) using ramp-shaped laser pulses and simultaneously measuring nanosecond-duration time-resolved X-ray diffraction, we found that solid carbon retains the diamond structure far beyond its regime of predicted stability. The results confirm predictions that the strength of the tetrahedral molecular orbital bonds in diamond persists under enormous pressure, resulting in large energy barriers that hinder conversion to more-stable high-pressure allotropes1,2, just as graphite formation from metastable diamond is kinetically hindered at atmospheric pressure. This work nearly doubles the highest pressure at which X-ray diffraction has been recorded on any material.

DOI: 10.1038/s41586-020-03140-4

Source: https://www.nature.com/articles/s41586-020-03140-4