意大利萨皮恩扎大学Bove Livia Eleonora研究团队取得一项新突破。他们报道利用准弹性中子散射观测塑性冰VII。2025年2月12日出版的《自然》发表了这项成果。

据悉，水是宇宙中含量第三多的分子，也是冰冷的卫星、巨行星以及类似天王星和海王星的系外行星内部的关键成分。由于其独特的分子结构和灵活的氢键，很容易适应广泛的压力和温度，水形成许多晶体和无定形相。与行星内部的高压和高温最相关的是冰VII4，模拟已经确定了沿其融化曲线存在所谓的塑性相，其中单个分子在固体中占据固定位置，但可以像液体中一样旋转。这种可塑冰还没有在实验中直接观察到。

该研究团队提出了准弹性中子散射（QENS）测量，在450至600 K的温度和高达6 GPa的压力下进行，揭示了在冰VII中发现的体心立方（bcc）结构的存在，其中水分子表现出典型的液态水皮秒旋转动力学。与分子动力学模拟的比较表明，这种塑料冰不符合自由转子相，而是表现出快速的定向跳跃，正如在跳转子塑料晶体中观察到的那样。该课题组预计，他们对塑料冰VII的观察，将影响他们对冰行星地球动力学和大型冰卫星分化过程的理解。

附：英文原文

Title: Observation of Plastic Ice VII by Quasi-Elastic Neutron Scattering

Author: Rescigno, Maria, Toffano, Alberto, Ranieri, Umbertoluca, Andriambariarijaona, Leon, Gaal, Richard, Klotz, Stefan, Koza, Michael Marek, Ollivier, Jacques, Martelli, Fausto, Russo, John, Sciortino, Francesco, Teixeira, Jose, Bove, Livia Eleonora

Issue&Volume: 2025-02-12

Abstract: Water is the third most abundant molecule in the universe and a key component in the interiors of icy moons, giant planets, and Uranus- and Neptune-like exoplanets1–3. Owing to its distinct molecular structure and flexible hydrogen bonds that readily adapt to a wide range of pressures and temperatures, water forms numerous crystalline and amorphous phases4–6. Most relevant for the high pressures and temperatures of planetary interiors is ice VII4, and simulations have identified along its melting curve the existence of a so-called plastic phase7–12 where individual molecules occupy fixed positions as in a solid yet are able to rotate as in a liquid. Such plastic ice has not yet been directly observed in experiments. Here, we present quasi-elastic neutron scattering (QENS) measurements, conducted at temperatures between 450 and 600 K and pressures up to 6 GPa, that reveal the existence of a body centered cubic (bcc) structure, as found in ice VII, with water molecules exhibiting picosecond rotational dynamics typical for liquid water. Comparison with molecular dynamics simulations indicates that this plastic ice VII does not conform to a free rotor phase but rather exhibits rapid orientational jumps, as observed in jump-rotor plastic crystals13,14. We anticipate that our observation of plastic ice VII will impact our understanding of the geodynamics of icy planets and the differentiation processes of large icy moons.

DOI: 10.1038/s41586-025-08750-4

Source: https://www.nature.com/articles/s41586-025-08750-4