Researchers at the European X-ray Free-Electron Laser facility in Germany have achieved a significant breakthrough in material science by successfully synthesizing a solid gold hydride. This remarkable accomplishment was made possible by subjecting gold to extreme conditions, including pressures exceeding 40 gigapascals (GPa) and temperatures surpassing 2000 Kelvin, achieved through rapid heating with ultrafast X-ray pulses.
The process allowed hydrogen atoms to infiltrate the otherwise stable hexagonal close-packed lattice of gold, leading to the formation of a compound that is only stable at these elevated temperatures. As the sample cools, it reverts to conventional gold, highlighting the transient nature of this hydride under standard conditions.
This newly forged compound emerges near gold’s melting point, and advanced computer simulations have affirmed its structure. The simulations indicate a disordered arrangement of hydrogen within the lattice, allowing for rapid diffusion in a superionic state. Notably, the interactions between gold and hydrogen exhibit an unusual covalent character, a departure from typical metal-hydrogen bonding, attributed to gold’s high electronegativity.
The stability of this compound under extreme conditions suggests that its formation is driven by an entropy-controlled reaction. Once the temperature decreases, the hydride transforms back into standard face-centered cubic gold alongside molecular hydrogen gas. This behavior elucidates why previous attempts to discover gold hydrides had not met with success; the compound would disintegrate before it could be collected and analyzed under normal atmospheric conditions.
The implications of this discovery extend beyond just the characteristics of gold. It prompts chemists to reconsider the perceived chemical inertness of gold and indicates that other so-called ‘inert’ materials may exhibit unexpected chemical behaviors when subjected to similarly extreme environments of pressure and temperature. This research opens new avenues for exploration in the field of high-pressure chemistry and the synthesis of novel materials.
