Speaker
Description
1 IMPMC, CNRS-UMR 7590, Université P&M Curie, 75252 Paris, France
2 Physics Department, Università di Roma La Sapienza, piazzale Aldo Moro 5, 00196, Roma, Italy
3 LQM, Physics Department, Ecole Politecnique Federale Lausanne, Lausanne, Swiss.
Over the past decade, computer simulations [1–3] have predicted the existence of a novel and intriguing phase of water, termed "Plastic water." This phase was expected to emerge along the melting line between liquid water and ice VII, as well as in water mixtures under extreme pressure–temperature (p–T) conditions [4]. In this phase, water molecules remain organized in a regular crystalline lattice while retaining the freedom to reorient, resulting in a hybrid state between that of a solid and a liquid. While plasticity is commonly observed in crystals of globular molecules like methane—where rotational motion persists within the crystal at high temperatures prior to melting—its occurrence in water ice is highly unusual.
Beyond plastic ice, theoretical studies predict several exotic high-pressure phases of water with similar (bcc-type) streuctures but profoundly different proton dynamics: quantum tunneling in the symmetric phase, molecular reorientation in plastic ice, long-range proton diffusion in the superionic phase, among them. High-pressure quasielastic neutron scattering (HP-QENS) offers a uniquely sensitive probe of these dynamic processes, enabling direct observation and experimental confirmation of these elusive phases.
Our recent HP-QENS experiments under high pressure have unveiled varying degrees of plasticity in high-pressure ice phases [5], water–ammonia ice mixtures [6], salty ices [7], methane and hydrogen-filled ices [8,9], and confined amorphous ice [10]. In this talk, I will discuss how plastic water arises in diverse environments and under varying p–T conditions, how plasticity is linked to the “glassy” behavior of water, and the implications of the existence of plastic ices for the geodynamics of icy moons.
[1] J. L. Aragones and C. Vega, Journal of Chemical Physics 130, 244504 (2009);
[2] K. Himoto, M. Matsumoto and H. Tanaka, Phys. Chem. Chem. Phys., 13, 19876–19881 (2011);
[3] Hernandez, J.-A., Caracas, R.: Physical Review Letters 117(13), 135503 (2020) ;
[4] A. Hermann, N. W. Ashcroft, N.W., R. Hoffmann, PNAS 745-750 (2012);
[5] Rescigno, M., Toffano, A., Ranieri, U. et al. Observation of Plastic Ice VII by Quasi-Elastic Neutron Scattering, Nature (2025) in press https:// doi.org/10.1038/s41586-025-08750-4;
[6] H. Zhang, et al., The Journal of Physical Chemistry Letters 14(9) 2301 (2023);
[7] A. Nichols et al., Earth and Planetary Science Letters submitted (2025);
[8] U. Ranieri et al., PNAS 120 52 (2023);
[9] Di Cataldo et al., Phys. Rev. Letters. 133 23 (2024);
[10] M. Rescigno et al., J. Phys. Chem. B (2023) 127 (20), 4570-4576
