美國勞倫斯利弗莫爾國家實驗室A. Lazicki揭示了金剛石壓縮到2TPa后的亞穩性。相關研究成果于2021年1月27日發表在國際知名學術期刊《自然》。

碳碳是宇宙中第四大元素，對所有已知生命都是必不可少的。在地球上，碳可以以許多不同的同素異形體的存在，包括石墨、金剛石和富勒烯，而且長期以來一直預測，在壓力大于地球核心的壓力下，甚至可以存在更多的結構。

據預測，在多個TPa區間存在多種相，這對于精確模擬富含碳的外行星的內部非常重要。通過使用激光脈沖將固體碳壓縮到2TPa（2000萬個大氣壓；是地球壓力的五倍以上），并同時測量納秒持續時間的X射線衍射，發現固體碳保留了金剛石結構，遠遠超出其預期的穩定性。

研究結果表明，在巨大的壓力下，金剛石仍然存在四面體分子軌道鍵，導致了很大的能量勢壘，阻礙了向更穩定的高壓同素異形體的轉化，正如亞穩金剛石的石墨在大氣下形成是受到運動阻礙一樣。

該項工作使在任何材料上記錄X射線衍射的最高壓力幾乎翻倍。

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