Wicks June K, Singh Saransh, Millot Marius, Fratanduono Dayne E, Coppari Federica, Gorman Martin G, Ye Zixuan, Rygg J Ryan, Hari Anirudh, Eggert Jon H, Duffy Thomas S, Smith Raymond F
Dept. of Earth & Planetary Sciences, Johns Hopkins University, Baltimore, MD 21218, USA.
Lawrence Livermore National Laboratory, Livermore, CA 94550, USA.
Sci Adv. 2024 Jun 7;10(23):eadk0306. doi: 10.1126/sciadv.adk0306.
Magnesium oxide (MgO) is a major component of the Earth's mantle and is expected to play a similar role in the mantles of large rocky exoplanets. At extreme pressures, MgO transitions from the NaCl 1 crystal structure to a CsCl 2 structure, which may have implications for exoplanetary deep mantle dynamics. In this study, we constrain the phase diagram of MgO with laser-compression along the shock Hugoniot, with simultaneous measurements of crystal structure, density, pressure, and temperature. We identify the 1 to 2 phase transition between 397 and 425 gigapascal (around 9700 kelvin), in agreement with recent theory that accounts for phonon anharmonicity. From 425 to 493 gigapascal, we observe a mixed-phase region of B1 and B2 coexistence. The transformation follows the Watanabe-Tokonami-Morimoto mechanism. Our data are consistent with 2-liquid coexistence above 500 gigapascal and complete melting at 634 gigapascal. This study bridges the gap between previous theoretical and experimental studies, providing insights into the timescale of this phase transition.
氧化镁（MgO）是地球地幔的主要成分，预计在大型岩石系外行星的地幔中也会发挥类似作用。在极端压力下，MgO会从氯化钠（NaCl）晶体结构转变为氯化铯（CsCl）结构，这可能会对系外行星的深部地幔动力学产生影响。在本研究中，我们通过沿冲击绝热线进行激光压缩来确定MgO的相图，同时测量晶体结构、密度、压力和温度。我们确定了在397至425吉帕斯卡（约9700开尔文）之间发生从1到2的相变，这与最近考虑声子非简谐性的理论一致。在425至493吉帕斯卡之间，我们观察到B1和B2共存的混合相区域。这种转变遵循渡边-户科波-森本机制。我们的数据与500吉帕斯卡以上的双液相共存以及634吉帕斯卡时的完全熔化相一致。本研究弥合了先前理论和实验研究之间的差距，为这一相变的时间尺度提供了见解。
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