Researchers decipher structure of superionic water with X-ray laser

An international research group has discovered a previously unknown form of superionic water. The experimental proof was provided at the European XFEL, among other facilities, as the research facility in Hamburg announced.

The team from the University of Rostock, the Helmholtz-Zentrum Dresden-Rossendorf, and the Centre national de la recherche scientifique (CNRS) Ecole Polytechnique in Palaiseau has generated superionic water using the X-ray lasers of the European XFEL and the Linac Coherent Light Source (LCLS) at the Stanford Linear Accelerator Center (SLAC). This is an exotic, highly electrically conductive phase of water that may occur in the interior of ice giants like Uranus and Neptune. The team has published the results in the journal Nature Communications.

Superionic water only forms under extreme temperatures and pressures. In this state, hydrogen ions move through a solid lattice of oxygen atoms. The water is particularly electrically conductive in this state.

X-ray lasers bombard water

The researchers put water samples at the XFEL and LCLS into this state. To do this, the water was compressed to pressures of more than 1.5 million atmospheres and heated to a thousand degrees Celsius. Thanks to the ultra-short X-ray flashes, they were able to record the atomic structure within picoseconds.

This allowed the researchers to decipher the structure of superionic water. The oxygen atoms arrange themselves in both face-centered cubic and close-packed hexagonal patterns. Since both forms occur together, the oxygen atoms form a hybrid, disordered sequence. According to the researchers, this pattern can be made visible using high-power X-ray lasers like the XFEL.

It is suspected that superionic water occurs in the interior of ice giants like Uranus and Neptune in our solar system. Due to its high conductivity, their unusual magnetic fields could have originated from it. Given the large amount of water in the interior of Uranus and Neptune, superionic water could thus be the most common form of water in our solar system.

Remarkable properties of water

The results showed that superionic water can exhibit structural diversity similar to that of solid ice, the researchers shared. Ice forms many different crystal structures depending on pressure and temperature. Water repeatedly reveals "new and remarkable properties under extreme conditions."

The XFEL is currently one of the most powerful X-ray lasers in the world. It is both a gigantic microscope and a gigantic camera, enabling observations with high temporal and spatial resolution, such as imaging chemical reactions in real-time or simulating conditions inside planets or stars.

Since the beginning of December, the facility has been cooled down to operating temperature again after a six-month maintenance period. We were there one last time before that.

(wpl)