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Explanation of order and disorder of crystal ice



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Since ancient times, ice has been a fascinating substance with unique properties and has aroused people’s interest. Unlike most other materials, ice at very low temperatures is not ordered. The cooperation between the Italian National Institute of Advanced Management (SISSA), the Abdus Salam International Center for Theoretical Physics (ICTP), and the Rosario Institute of Physics (IFIR-UNR) was supported by the Italian National Center for Material Research The Research Committee (CNR-IOM) has made new theoretical breakthroughs in the reasons for this situation and the ways to make up for some missing orders. In that orderly state, the team of scientists described a very dark but very basic characteristic of low-temperature ice: ferroelectricity.The results are published in PNASIt may extend to the ice surface, which may be related to the accumulation of ice particles in interstellar space.

SISSA and ICTP physicist Alessandro Laio explained: “In an ideally ordered ice block, the hydrogen atoms of each water molecule should point in the same direction, just like the soldiers in front of them.”

; “If it is. In this case, the ice will exhibit a macroscopic polarization-it will be ferroelectric. On the contrary, even at very low temperatures, the water molecules in the ice will behave like unruly soldiers, and they are all moving towards Look in different directions.”

This abnormal behavior was discovered experimentally in the 1930s, and Linus Pauling immediately and famously explained that lack of discipline is the result of the “ice rule” constraint-every oxygen atom should be at all times Has two and only two protons to make it H2O. The difficult dynamics generated by this constraint will cause the sorting process to become infinitely slow. For example, in a platoon, each soldier has four neighbors, and two hands must be placed on the shoulders of two of them.

“It is not because of impurities or defects that play a significant role. Today, people still don’t know whether the proton sequence and the ferroelectricity of large crystalline ice actually exist, or whether it is a fiction of imagination, because experiments and simulations cannot be SISSA, ICTP and Erio Tosatti, a physicist at CNR-IOM Democritos, points out.

Impurities, such as a KOH instead of H2In fact, it is well known that O allows the ordering process to nucleate, while ice becomes orderly and ferroelectric at extremely low temperatures, albeit only partially and slowly. Once again, people suspect that the “ice rule” is behind the slow process, but the exact way it works is unclear.

Alessandro Laio and Erio Tosatti, associate members of ICTP, and Jorge Lasave and Sergio Koval of IFIR-UNR in Argentina, jointly designed theoretical models and strategies to explain the behavior of pure ice and doped ice.

The scientist explained: “According to this model, once impurities are introduced into the initial non-equilibrium low-temperature disordered state, it can serve as the seed of the ordered phase, but in a special way: The impurities start looking in the right direction, but only those before or after the impurities. Therefore, at the end of the process, only a series of soldiers in the platoon will be ordered.” This highly atypical process has many features that can explain the true doping Slow and incomplete occurrence of ferroelectric sequence in miscellaneous ice.

Tosatti and Laio concluded: “Although current research is limited to bulk ice, the outstanding mechanism is likely to extend to the ice surface, where ordered proton strings may nucleate at low temperatures, which explains the well-known small number of local Ferroelectric polarization is also believed to be related to the accumulation of ice particles in interstellar space.”



More information:
J. Lasave et al. In the atypical nucleation of ferroelectricity in ice, proton strings and rings, Proceedings of the National Academy of Sciences (2020). DOI: 10.1073 / pnas.2018837118

Provided by the International Institute for Advanced Studies (SISSA)



Citation: Explained (December 29, 2020) the order and disorder in crystal ice, from https://phys.org/news/2020-12-disorder-crystal-ice on December 30, 2020 .html search

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