冲击压缩超离子水冰的纳秒 X 射线衍射,Nature

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冲击压缩超离子水冰的纳秒 X 射线衍射
Nature ( IF 50.5 ) Pub Date : 2019-05-01 , DOI: 10.1038/s41586-019-1114-6
Marius Millot ₁ , Federica Coppari ₁ , J Ryan Rygg _{1,

2} , Antonio Correa Barrios ₁ , Sebastien Hamel ₁ , Damian C Swift ₁ , Jon H Eggert ₁

Affiliation

自 1912 年布里奇曼发现五种固态水 (H2O) 冰相 1 以来，对 H2O 非凡多态性的研究已经记录了超过 17 种晶体和几种非晶冰结构 2,3，以及丰富的亚稳态和动力学效应 4,5。这种独特的行为部分是由于弱分子间氢键的几何受挫和轻氢离子（质子）的巨大量子运动。特别有趣的是，当受到超过 100 吉帕斯卡的极端压力和超过 2,000 开尔文的高温时，H2O 会变成超离子 6-12（液体状质子通过氧的固体晶格扩散）的预测。数值模拟表明，质子通过氧固体晶格 (1) 的空位的特征扩散产生了超过 100 西门子/厘米的惊人高离子电导率，即几乎与典型的金属（电子）电导率一样高， (2) 将冰融化温度 7-13 大大提高到几千开尔文，并且 (3) 有利于具有密堆积氧晶格的新冰结构 13-15。由于在实验室中限制如此高温和密集的 H2O 极具挑战性，因此实验数据很少。最近沿水冰 VII 的 Hugoniot 曲线（激波态轨迹）的光学测量显示出超离子传导和熔化的热力学特征的证据，但没有证实超离子冰的微观结构。在这里，我们使用激光驱动的冲击波将液态水样品同时压缩和加热至 100-400 吉帕斯卡和 2,000-3,000 开尔文。原位 X 射线衍射测量表明，在这些条件下，水在几纳秒内凝固成纳米大小的冰粒，这些冰粒显示出超离子水冰的结晶氧晶格的明确证据。X 射线衍射数据还使我们能够记录冰在这些极端条件下的可压缩性以及从以体心为中心的立方冰相（可能是冰 X）到新的以面为中心的相变的温度和压力诱导的相变。立方的超离子冰相，我们将其命名为冰 XVIII2,17。在数百万个大气压和数千度的温度下记录了 H2O 的原子结构，

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Nanosecond X-ray diffraction of shock-compressed superionic water ice

Since Bridgman’s discovery of five solid water (H2O) ice phases1 in 1912, studies on the extraordinary polymorphism of H2O have documented more than seventeen crystalline and several amorphous ice structures2,3, as well as rich metastability and kinetic effects4,5. This unique behaviour is due in part to the geometrical frustration of the weak intermolecular hydrogen bonds and the sizeable quantum motion of the light hydrogen ions (protons). Particularly intriguing is the prediction that H2O becomes superionic6–12—with liquid-like protons diffusing through the solid lattice of oxygen—when subjected to extreme pressures exceeding 100 gigapascals and high temperatures above 2,000 kelvin. Numerical simulations suggest that the characteristic diffusion of the protons through the empty sites of the oxygen solid lattice (1) gives rise to a surprisingly high ionic conductivity above 100 Siemens per centimetre, that is, almost as high as typical metallic (electronic) conductivity, (2) greatly increases the ice melting temperature7–13 to several thousand kelvin, and (3) favours new ice structures with a close-packed oxygen lattice13–15. Because confining such hot and dense H2O in the laboratory is extremely challenging, experimental data are scarce. Recent optical measurements along the Hugoniot curve (locus of shock states) of water ice VII showed evidence of superionic conduction and thermodynamic signatures for melting16, but did not confirm the microscopic structure of superionic ice. Here we use laser-driven shockwaves to simultaneously compress and heat liquid water samples to 100–400 gigapascals and 2,000–3,000 kelvin. In situ X-ray diffraction measurements show that under these conditions, water solidifies within a few nanoseconds into nanometre-sized ice grains that exhibit unambiguous evidence for the crystalline oxygen lattice of superionic water ice. The X-ray diffraction data also allow us to document the compressibility of ice at these extreme conditions and a temperature- and pressure-induced phase transformation from a body-centred-cubic ice phase (probably ice X) to a novel face-centred-cubic, superionic ice phase, which we name ice XVIII2,17.The atomic structure of H2O is documented at several million atmospheres of pressure and temperatures of several thousand degrees, revealing shockwave-induced ultrafast crystallization and a novel water ice phase, ice XVIII, with exotic superionic properties.

更新日期：2019-05-01

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