Giant lasers crystallize water with shockwaves, revealing the atomic structure of superionic ice

Scientists from Lawrence Livermore National Laboratory (LLNL) used las las las automats à flash-freeze exotic superionic phase and record X-ray diffraction patterns to identify its atomic structure for the very first time-all in just a few billionths of a second. The findings are reported today in Nature.

In 1988, scientists first predicted that water would transition to an exotic state of matter characterized by the coexistence of a solid state of oxygen and liquid-like hydrogen-superionic. -rich giant planets like Uranus and Neptune. These predictions remained in place until 2018, when a team led by scientists from LLNL presented the first experimental evidence for this strange state of water.

Now, the LLNL scientists describe new results. Using laser-driven shockwaves and in-situ X-ray diffraction, they observe the nucleation of a crystalline lattice of oxygen in a few billionths of a second, revealing for the first time microscopic structure of superionic ice.

The data also provides further insight into the interior of giant planets.

"We wanted to determine the atomic structure of superionic water," said LLNL physicist Federica Coppari, co-lead author of the paper. "But given the extreme conditions in which this state of the art is predicted to be stable, it is a very difficult task, which requires an innovative experimental design."

The researchers performed a series of experiments at the Omega Laser Facility at the University of Rochester's Laser Energetics Laboratory (LLE). They used six giant laser beams to generate a sequence of shockwaves of progressively increasing pressure to thin layers of liquid water to extreme pressures (100-400 gigapascals (GPa), or 1-4 million times Earth's atmospheric pressure) and temperatures ( 3,000-5,000 degrees Fahrenheit).

"We thought it would be a good idea to have some ice, but it was not certain that the ice crystals would actually grow in the second half of a second time." said LLNL physicist and co-lead author Marius Millot.

To document the crystallization and identification of the atomic structure, the team blasted a tiny iron foil with 16 additional laser pulses to create a hot plasma, which generated a flash of X-rays domain of superionic ice.

"The X-ray diffraction patterns we measured are an unambiguous signature for dense ice crystals during the ultrafast shockwave compression demonstrating that nucleation of solid ice from liquid water is fast enough to be observed in the nanosecond timescale of the experiment," Coppari said.

"In the previous work we could only measure macroscopic properties such as internal energy and temperature," Millot added. "Therefore, we conceive of a new and different experiment to document the atomic structure. for the existence of superionic ice we last year. "

The atomic structure for dense water ice.

"Ih, II, III, up to XVII," Coppari said. "So, we propose to call the new f.c.c solid form 'ice XVIII.' Computer simulations have proposed a number of different crystalline structures for superionic ice.

The team's data has profound implications for the interior of the giant planets. Since superionic ice is ultimately a solid, the idea of ​​these planets.

"Because water ice at Uranus and Neptune's interior conditions has a crystalline lattice, we argue that it is more likely that this will be the case. to the earth's mantle, which is made of solid rock, yet flows and supports large-scale convective motions on the very long geological timescales, "Millot said. "This can dramatically affect our understanding of the internal structure and evolution of the giant planets, plus their numerous extrasolar cousins."