Scientists unexpectedly create solid gold hydride under extreme pressure and heat

Unexpected Alchemy: Scientists Forge Solid Gold Hydride Under Extreme Conditions

In a groundbreaking revelation that defies conventional chemistry, an international team of researchers, spearheaded by scientists from the U.S. Department of Energy's SLAC National Accelerator Laboratory, has achieved a remarkable feat: the creation of the first-ever solid binary gold hydride. This exotic compound, composed solely of gold and hydrogen atoms, emerged not from a directed effort to synthesize new materials, but as a surprising byproduct of experiments designed to understand diamond formation.

From Diamond Dreams to Golden Surprises

The initial objective was to explore the transformation of hydrocarbons—molecules rich in carbon and hydrogen—into diamonds under immense pressure and searing heat. To facilitate this process, researchers placed hydrocarbon samples on an ultra-thin layer of gold foil. This gold was intended to act as a heat sink and radiation absorber, efficiently transferring the energy from intense X-ray pulses generated by the European X-ray Free-Electron Laser (XFEL) in Germany to the less absorptive hydrocarbons. However, in a stunning turn of events, alongside the anticipated formation of diamond lattices, the scientists observed the unexpected emergence of gold hydride.

"This was unexpected, as gold is typically chemically very boring and inert, which is why we use it as an X-ray absorber in these experiments."

This serendipitous discovery, as lead author and SLAC staff scientist Mango Frost articulated, underscores the potential for uncovering novel chemical reactions in extreme environments. "These results suggest that under extreme conditions where temperature and pressure effects start to compete with traditional chemical processes, it's potentially possible to unlock many new chemical reactions, and these exotic compounds can be formed," Frost noted. The formation of gold hydride occurred at pressures exceeding 40 gigapascals (GPa) and temperatures of approximately 1926.8 degrees Celsius when pre-compressed gold within the hydrocarbons was heated by the XFEL.

Unlocking the Secrets of Dense Hydrogen

The experimental setup involved compressing hydrocarbon samples to pressures far exceeding those found in Earth's mantle, using a diamond anvil cell. Subsequently, these compressed samples were subjected to powerful X-ray pulses from the XFEL, reaching temperatures of nearly 1900 degrees Celsius. By analyzing X-ray scattering patterns, the researchers meticulously tracked structural changes. While the carbon atoms rearranged into the coveted diamond lattice, the hydrogen atoms surprisingly reacted with the gold foil, forging the gold hydride compound. Crucially, under these extreme experimental conditions, the hydrogen atoms entered a dense "superionic" state. In this state, hydrogen atoms move freely within a rigid gold lattice, significantly enhancing the hydride's conductivity and offering an unprecedented window into the behavior of matter under immense pressure and heat.

Implications for Planetary Science and Fusion Energy

Studying hydrogen under such dense conditions is typically a formidable challenge due to its poor X-ray scattering properties. However, the superionic hydrogen's interaction with the much heavier gold atoms allowed scientists to observe its influence on the X-ray scattering of the gold lattice. This breakthrough offers a powerful new method for studying dense atomic hydrogen in environments that are otherwise inaccessible to experimental research. The implications are vast, potentially shedding light on the composition of planetary interiors, such as the cores of gas giants, and offering deeper insights into the thermonuclear fusion processes occurring within stars like our Sun. Furthermore, this research could pave the way for advancements in developing controlled fusion energy technologies on Earth.

A New Chapter in Chemistry

The discovery challenges the long-held notion of gold's inertness. The research demonstrates that gold can, under extreme pressure and temperature, form a stable hydride. Interestingly, this hydride appears to be stable only under these extraordinary conditions, dissociating back into gold and hydrogen upon cooling. The findings, published in the prestigious journal *Angewandte Chemie International Edition*, mark a significant milestone in our understanding of exotic material synthesis and the fundamental nature of chemical reactions at the limits of physical possibility.