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

Last update: January 24, 2019

Our new research paper has been published.

 

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)

DOI:10.1063/1.5083021

 

Although the most stable phase in the negative pressure region (in a stretched state) is a gas phase, the crystal can also exist as a metastable state. Regarding water, crystal ice XVI with lower density than ordinary ice was made by special manufacturing method in 2014 and it is expected to be stable under  negative pressure. Therefore, attention has been paid to searching for new low density ices. In our previous paper, we showed that there are countless crystal structures that becomes stable under negative pressure, and among them the aeroice is predicted to be stable over an extremely wide temperature-pressure range. However, it was also predicted that the ice with many such pores is brittle in structure, and stability can not be evaluated correctly by conventional evaluation method.

In this study, not only the thermodynamic stability of each crystal structure but also the mechanical stability were evaluated, and a more accurate negative pressure ice phase diagram was created. It turned out that many crystal structures evaluated as thermodynamically stable are easily disintegrated with temperature and can not maintain the crystal structure and the phase diagram is complicated at low temperature and becomes simple as the temperature becomes higher. Also, as the negative pressure is made extremely large, many low-density ice will collapse and relatively dense and durable structures such as ice lh and ice XVI will survive to the end, so the same phase will be on the phase diagram I found an interesting phenomenon that it appeared more than twice. It is a paper that predicted by simulation what can happen under the condition of negative pressure, which is almost inaccessible in experiments.

Figure: Phase diagram of ice under negative pressures.