Nanosecond X-ray diffraction of shock-compressed superionic water ice
Nanosecond X-ray diffraction of shock-compressed superionic water ice
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DOI：
10.1038/s41586-019-1114-6
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发表时间：
2019-05-09
期刊：
影响因子：
64.8
通讯作者：
Eggert, Jon H.
中科院分区：
文献类型：
--
作者：
Millot, Marius;Coppari, Federica;Eggert, Jon H.
自1912年Bridgman发现五种固体水（H2O）冰相(1)以来，对H2O非凡多态性的研究已经记录了超过17种结晶和几种非晶态冰结构（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挫折和轻氢离子（质子）的相当大的量子运动。特别有趣的是，当受到超过100千兆帕斯卡的极端压力和超过2000开尔文的高温时，水会变成超离子（6-12）——具有液体状质子扩散穿过氧的固体晶格。数值模拟表明，质子通过氧固体晶格空位置的特征扩散(1)产生了令人惊讶的高离子电导率，高于每厘米100西门子，即几乎与典型的金属（电子）电导率一样高，(2)大大提高了冰的融化温度（7-13）到几千开尔文，(3)有利于具有紧密堆积的氧晶格的新冰结构（13-15）。由于在实验室中限制如此高温和致密的水是极具挑战性的，实验数据很少。最近沿着水冰的Hugoniot曲线（激波状态轨迹）的光学测量显示了超离子传导和熔化的热力学特征的证据（16），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同时压缩和加热液态水样品到100-400千兆帕斯卡和2000 - 3000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，这为超离子水冰的结晶氧晶格提供了明确的证据。X射线衍射数据还允许我们记录冰在这些极端条件下的可压缩性，以及温度和压力诱导的相变，从体心立方冰相（可能是冰X）到新的面心立方超离子冰相，我们将其命名为冰XVIII2,17。
Since Bridgman's discovery of five solid water (H2O) ice phases(1) in 1912, studies on the extraordinary polymorphism of H2O have documented more than seventeen crystalline and several amorphous ice structures(2,3), as well as rich metastability and kinetic effects(4,5). 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 superionic(6-12)-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 temperature(7-13) to several thousand kelvin, and (3) favours new ice structures with a close-packed oxygen lattice(13-15). 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 melting(16), 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.