Dielectric Anomalies in Crystalline Ice: Indirect Evidence of the Existence of a Liquid鈥揕iquid Critical Point in H2O

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• 作者：Fei Yen ; Zhenhua Chi ; Adam Berlie ; Xiaodi Liu ; Alexander F. Goncharov
• 刊名：Journal of Physical Chemistry C
• 出版年：2015
• 出版时间：September 3, 2015
• 年：2015
• 卷：119
• 期：35
• 页码：20618-20622
• 全文大小：359K
• ISSN：1932-7455

文摘

The phase diagram of H₂O is extremely complex; in particular, it is believed that a second critical point exists deep below the supercooled water (SCW) region where two liquids of different densities coexist. The problem, however, is that SCW freezes at temperatures just above this hypothesized liquid鈥搇iquid critical point (LLCP), so direct experimental verification of its existence has yet to be realized. Here, we report two anomalies in the complex dielectric constant during warming in the form of a peak anomaly near T_p = 203 K and a sharp minimum near T_m = 210 K from ice samples prepared from SCW under hydrostatic pressures of up to 760 MPa. The same features were observed about 4 K higher in heavy ice. T_p is believed to be associated with the nucleation process of metastable cubic ice Ic, and T_m is the transitioning of ice Ic to either ice Ih or II depending on the pressure. Given that T_p and T_m are nearly isothermal, present up to at least 620 MPa, and end as a critical point near 33鈥?0 MPa, it is deduced that two types of SCWs with different density concentrations exist, which affects the surface energy of ice Ic nuclei in the 鈥渘o man鈥檚 land鈥?region of the phase diagram. Our results are consistent with the LLCP theory and suggest that a metastable critical point exists in the region of 33鈥?0 MPa and T_c 鈮?210 K.