Turneaure Stefan J, Sharma Surinder M, Volz Travis J, Winey J M, Gupta Yogendra M
Institute for Shock Physics, Washington State University, Pullman, WA 99164, USA.
Department of Physics and Astronomy, Washington State University, Pullman, WA 99164, USA.
Sci Adv. 2017 Oct 27;3(10):eaao3561. doi: 10.1126/sciadv.aao3561. eCollection 2017 Oct.
The graphite-to-diamond transformation under shock compression has been of broad scientific interest since 1961. The formation of hexagonal diamond (HD) is of particular interest because it is expected to be harder than cubic diamond and due to its use in terrestrial sciences as a marker at meteorite impact sites. However, the formation of diamond having a fully hexagonal structure continues to be questioned and remains unresolved. Using real-time (nanosecond), in situ x-ray diffraction measurements, we show unequivocally that highly oriented pyrolytic graphite, shock-compressed along the axis to 50 GPa, transforms to highly oriented elastically strained HD with the (100) plane parallel to the graphite basal plane. These findings contradict recent molecular dynamics simulation results for the shock-induced graphite-to-diamond transformation and provide a benchmark for future theoretical simulations. Additionally, our results show that an earlier report of HD forming only above 170 GPa for shocked pyrolytic graphite may lead to incorrect interpretations of meteorite impact events.
自1961年以来，冲击压缩下的石墨向金刚石转变一直备受科学界广泛关注。六方金刚石（HD）的形成尤其令人感兴趣，因为它预计比立方金刚石更硬，并且在地球科学中作为陨石撞击地点的标记物而被使用。然而，具有完全六方结构的金刚石的形成仍然受到质疑且尚未得到解决。通过实时（纳秒级）原位X射线衍射测量，我们明确表明，沿c轴冲击压缩至50 GPa的高度取向热解石墨会转变为高度取向的弹性应变HD，其（100）面与石墨基面平行。这些发现与最近关于冲击诱导石墨向金刚石转变的分子动力学模拟结果相矛盾，并为未来的理论模拟提供了一个基准。此外，我们的结果表明，先前关于热解石墨在冲击下仅在170 GPa以上形成HD的报告可能会导致对陨石撞击事件的错误解读。
