超硬材料網(wǎng)

美國(guó)勞倫斯利弗莫爾國(guó)家實(shí)驗(yàn)室A. Lazicki揭示了金剛石壓縮到2TPa后的亞穩(wěn)性。相關(guān)研究成果于2021年1月27日發(fā)表在國(guó)際知名學(xué)術(shù)期刊《自然》。

碳碳是宇宙中第四大元素，對(duì)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(zhǎng)期以來(lái)一直預(yù)測(cè)，在壓力大于地球核心的壓力下，甚至可以存在更多的結(jié)構(gòu)。

據(jù)預(yù)測(cè)，在多個(gè)TPa區(qū)間存在多種相，這對(duì)于精確模擬富含碳的外行星的內(nèi)部非常重要。通過(guò)使用激光脈沖將固體碳?jí)嚎s到2TPa（2000萬(wàn)個(gè)大氣壓；是地球壓力的五倍以上），并同時(shí)測(cè)量納秒持續(xù)時(shí)間的X射線衍射，發(fā)現(xiàn)固體碳保留了金剛石結(jié)構(gòu)，遠(yuǎn)遠(yuǎn)超出其預(yù)期的穩(wěn)定性。

研究結(jié)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(dǎo)致了很大的能量勢(shì)壘，阻礙了向更穩(wěn)定的高壓同素異形體的轉(zhuǎn)化，正如亞穩(wěn)金剛石的石墨在大氣下形成是受到運(yùn)動(dòng)阻礙一樣。

該項(xiàng)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