The Curious Corner

Scientists at the SLAC National Accelerator Laboratory have made a surprising discovery that has shaken conventional ideas of chemical science. For the first time in history, they have created a new compound called gold hydride, which is composed only of gold and hydrogen

Originally, their purpose was to understand how hydrocarbons turn into diamonds at high heat and pressure. That's why the European XFEL lab used thin gold foil with hydrocarbons just to absorb heat. But during the experiment, gold hydride was created along with diamond, which surprised scientists.

Gold is generally known as a chemically inert metal. That's why gold doesn't have many compounds. So the reaction of hydrogen with gold is completely unexpected. Studies have shown that at high pressures and temperatures, conventional chemical laws are broken and new types of compounds can be formed.

In this experiment, scientists compressed hydrocarbons with pressures higher than the pressure of the Earth's mantle and heated them to more than 3,500 degrees Fahrenheit. As a result, hydrogen goes into a superionic state, where it spreads freely inside the gold crystal lattice. In this situation, the electrical conductivity of gold hydride increases, which gives an idea of the properties of new types of materials.

This discovery is not only an example of the creation of new compounds, but also creates new opportunities for the study of dense hydrogen. Such hydrogen is found deep inside the planet and in the interior of stars. So if it is created in the laboratory, we can get new information about the formation of planets, nuclear fusion processes and future fusion energy developments.

While gold hydride is stable only in extreme conditions and breaks down when cooled. The researchers found in the simulation that more hydrogen could be added to it under increased pressure. This method will also help create other strange compounds in the future. (Scientist)

The researchers were studying how long it takes hydrocarbons, compounds made of carbon and hydrogen, to form diamonds under extremely high pressure and heat. In their experiments at the European XFEL (X-ray Free-Electron Laser) in Germany, the team studied the effect of those extreme conditions in hydrocarbon samples with an embedded gold foil, which was meant to absorb the X-rays and heat the weakly absorbing hydrocarbons. To their surprise, they not only saw the formation of diamonds, but also discovered the formation of gold hydride.

"It was unexpected because gold is typically chemically very boring and unreactive -- that's why we use it as an X-ray absorber in these experiments," said Mungo Frost, staff scientist at SLAC who led the study. "These results suggest there's potentially a lot of new chemistry to be discovered at extreme conditions where the effects of temperature and pressure start competing with conventional chemistry, and you can form these exotic compounds."

The results, published in Angewandte Chemie International Edition, provide a glimpse of how the rules of chemistry change under extreme conditions like those found inside certain planets or hydrogen-fusing stars.

Studying dense hydrogen

In their experiment, the researchers first squeezed their hydrocarbon samples to pressures greater than those within Earth's mantle using a diamond anvil cell. Then, they heated the samples to over 3,500 degrees Fahrenheit by hitting them repeatedly with X-ray pulses from the European XFEL. The team recorded and analyzed how the X-rays scattered off the samples, which allowed them to resolve the structural transformations within.

As expected, the recorded scattering patterns showed that the carbon atoms had formed a diamond structure. But the team also saw unexpected signals that were due to hydrogen atoms reacting with the gold foil to form gold hydride.

Under the extreme conditions created in the study, the researchers found hydrogen to be in a dense, "superionic" state, where the hydrogen atoms flowed freely through the gold's rigid atomic lattice, increasing the conductivity of the gold hydride.

Hydrogen, which is the lightest element of the periodic table, is tricky to study with X-rays because it scatters X-rays only weakly. Here, however, the superionic hydrogen interacted with the much heavier gold atoms, and the team was able to observe hydrogen's impact on how the gold lattice scattered X-rays. "We can use the gold lattice as a witness for what the hydrogen is doing," Mungo said

The gold hydride offers a way to study dense atomic hydrogen under conditions that might also apply to other situations that are experimentally not directly accessible. For example, dense hydrogen makes up the interiors of certain planets, so studying it in the lab could teach us more about those foreign worlds. It could also provide new insights into nuclear fusion processes inside stars like our sun and help develop technology to harness fusion energy here on Earth.

Exploring new chemistry

In addition to paving the way for studies of dense hydrogen, the research also offers an avenue for exploring new chemistry. Gold, which is commonly regarded as an unreactive metal, was found to form a stable hydride at extremely high pressure and temperature. In fact, it appears to be only stable at those extreme conditions as when it cools down, the gold and hydrogen separate. The simulations also showed that more hydrogen could fit in the gold lattice at higher pressure.

"These results suggest there's potentially a lot of new chemistry to be discovered at extreme conditions where the effects of temperature and pressure start competing with conventional chemistry, and you can form these exotic compounds." Mungo Frost SLAC staff scientist

The simulation framework could also be extended beyond gold hydride. "It's important that we can experimentally produce and model these states under these extreme conditions," said Siegfried Glenzer, High Energy Density Division director and professor for photon science at SLAC and the study's principal investigator. "These simulation tools could be applied to model other exotic material properties in extreme conditions."

The team also included researchers from Rostock University, DESY, European XFEL, Helmholtz-Zentrum Dresden-Rossendorf, Frankfurt University and Bayreuth University, all in Germany; the University of Edinburgh, UK; the Carnegie Institution for Science, Stanford University and the Stanford Institute for Materials and Energy Sciences (SIMES). Parts of this work were supported by the DOE Office of Science.

Journal Reference:

1. Mungo Frost, Kilian Abraham, Alexander F. Goncharov, R. Stewart McWilliams, Rachel J. Husband, Michal Andrzejewski, Karen Appel, Carsten Baehtz, Armin Bergermann, Danielle Brown, Elena Bykova, Anna Celeste, Eric Edmund, Nicholas J. Hartley, Konstantin Glazyrin, Heinz Graafsma, Nicolas Jaisle, Zuzana Konôpková, Torsten Laurus, Yu Lin, Bernhard Massani, Maximilian Schörner, Maximilian Schulze, Cornelius Strohm, Minxue Tang, Zena Younes, Gerd Steinle‐Neumann, Ronald Redmer, Siegfried H. Glenzer. Synthesis of Gold Hydride at High Pressure and High Temperature. Angewandte Chemie International Edition, 2025; DOI: