Takahiro Matsui, Takuma Yagasaki, Masakazu Matsumoto, and Hideki Tanaka

Phase diagram of ice polymorphs under negative pressure considering the limits of mechanical stability

J. Chem. Phys. 150, 041102 (2019)




The most stable phase in the negative pressure region (the stretched state of a substance) is the gas phase, but the crystal can also exist as a metastable state. In 2014, crystal ice XVI, which has a lower density than normal ice, was produced by a special process, and is expected to become stable under negative pressure. Therefore, attention is focused on finding new low-density ice. In our previous paper (MHYMT2017), we predicted that there are numerous crystal structures that are stable under negative pressure, and that the designed ice aeroice is stable over a very wide temperature and pressure range. However, it was also predicted that ice with many such pores would be fragile in structure, and the stability could not be correctly evaluated by conventional evaluation methods.

In this study, we evaluated not only the thermodynamic stability but also the mechanical stability of each crystal structure, and created a more accurate negative pressure ice phase diagram. It was found that many crystal structures evaluated to be thermodynamically stable collapse easily with temperature and cannot maintain the crystal structure, and that phase diagrams are complicated at low temperatures and simpler at high temperatures. At very high negative pressures, many low-density ice decays, and the same phase appears more than once on the phase diagram to allow relatively dense and robust structures such as ice lh and ice XVI to survive to the end. It is a paper that predicted what could happen under the condition of negative pressure, which is almost inaccessible in experiments, by simulation.

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