Structure and properties of two superionic ice phases
Structure and properties of two superionic ice phases
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DOI：
10.1038/s41567-021-01351-8
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发表时间：
2021-10
期刊：
影响因子：
19.6
通讯作者：
V. Prakapenka;N. Holtgrewe;S. Lobanov;A. Goncharov
中科院分区：
文献类型：
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作者：
V. Prakapenka;N. Holtgrewe;S. Lobanov;A. Goncharov
在水的相图中，预测了在高压下稳定的氧亚晶格中具有高迁移率质子的上声子冰。然而，从理论和实验上确定上音速冰的存在和熔化线的位置一直具有挑战性，根据所采用的技术和对数据的解释，得出了相互矛盾的结果。在这里，我们报道了高压和高温同步X射线衍射和光谱测量的水在激光加热的钻石顶压室，并揭示了一级相变到冰的身体中心和面中心的立方氧晶格。根据明显的密度、增加的光学传导性和大大降低的熔化热焓，我们将这些观测到的结构归类为理论预测的上声子冰相。我们的测量确定了上声子冰相和融化线的压力-温度稳定场，表明在海王星和天王星等富水的巨型行星中存在以面心为中心的立方上声子冰。本文所确定的熔点温度高于静态压缩实验所确定的温度，但与理论计算和冲击波实验数据相一致。
In the phase diagram of water, superionic ices with highly mobile protons within the stable oxygen sublattice have been predicted at high pressures. However, the existence of superionic ices and the location of the melting line have been challenging to determine from both theory and experiments, yielding contradictory results depending on the employed techniques and the interpretation of the data. Here we report high-pressure and high-temperature synchrotron X-ray diffraction and optical spectroscopy measurements of water in a laser-heated diamond anvil cell and reveal first-order phase transitions to ices with body-centred and face-centred cubic oxygen lattices. Based on the distinct density, increased optical conductivity and the greatly decreased fusion enthalpies, we assign these observed structures to the theoretically predicted superionic ice phases. Our measurements determine the pressure–temperature stability fields of superionic ice phases and the melting line, suggesting the presence of face-centred cubic superionic ice in water-rich giant planets, such as Neptune and Uranus. The melting line determined here is at higher temperatures than previously determined in static compression experiments, but it is in agreement with theoretical calculations and data from shock-wave experiments.