By Lisa Zyga
The researchers, including Hai-Xia Zhao, Xiang-Jian Kong and La-Sheng Long, along with their coauthors from Xiamen University in Xiamen, China, and Hui Li and Xiao Cheng Zeng from the University of Nebraska in the US, have published their study in a recent issue of the Proceedings of the National Academy of Sciences.
Every water molecule carries a tiny electric field. But because water molecules usually freeze in a somewhat random arrangement, with their bonds pointing in different directions, the ice’s total electric field tends to cancel out. In contrast, the bonds in ferroelectric ice all point in the same direction at low enough temperatures, so that it has a net polarization in one direction that produces an electric field.
Ferroelectric ice is thought to be extremely rare; in fact, scientists are still investigating whether or not pure three-dimensional ferroelectric ice exists in nature. Some researchers have proposed that ferroelectric ice may exist on Uranus, Neptune, or Pluto. Creating pure 3D ferroelectric ice in the laboratory seems next to impossible, since it would take an estimated 100,000 years to form without the assistance of catalysts. So far, all ferroelectric ices produced in the laboratory are less than three dimensions and in mixed phases (heterogeneous).
In the new study, the scientists have synthesized a one-dimensional, single-phase (homogeneous) ferroelectric ice by freezing a one-dimensional water ‘wire.’ As far as the scientists know, this is the first single-phase ferroelectric ice synthesized in the laboratory.
To create the water wire, the researchers designed very thin nanochannels that can hold just 96 H2O molecules per crystalline unit cell. By lowering the temperature from a starting point of 350 K (77°C, 171°F), they found that the water wire undergoes a phase transition below 277 K (4°C, 39°F), transforming from 1D liquid to 1D ice. The ice also exhibits a large dielectric anomaly at this temperature and at 175 K (-98°C, -144°F).