Researchers have captured the most detailed look yet at how gold’s atomic structure changes under some of the highest pressures ever achieved in a laboratory.
The new findings offer rare insight into how matter behaves deep inside giant planets and in the high-pressure environments used for fusion research.
The experiments were led by Lawrence Livermore National Laboratory (LLNL) in collaboration with other institutions. By compressing gold to pressures about 10 million times Earth’s atmospheric pressure, the team made the highest-pressure structural measurement ever recorded for the material.
These observations address long-standing inconsistencies about gold’s behavior under extreme compression and refine its use as a reference material in high-pressure science.
“These experiments uncover the atomic rearrangements that occur at some of the most extreme pressures achievable in laboratory experiments,” said LLNL scientist and study author Amy Coleman.
Pressures inside giant planets can exceed one million times Earth’s atmospheric pressure, forcing materials into unfamiliar atomic arrangements. Replicating those conditions on Earth requires facilities capable of delivering intense and precisely shaped energy pulses.
To reach the required pressure range, the researchers used tailored laser pulses at the National Ignition Facility (NIF) and the OMEGA EP Laser System at the University of Rochester.
These pulses compressed gold samples rapidly while keeping temperatures lower than in many high-pressure experiments, allowing the metal to remain in a solid state. The team then used X-ray diffraction to capture atomic-scale snapshots within a billionth of a second.
Coleman noted that “only recently have facilities like NIF could both create these pressures and to take a snapshot of what happens to atoms inside the sample.”
She added that this is the first definitive look at gold’s crystal structure at such extreme compression and that the results “finally resolve long-standing disagreements between theory and experiment.”
Under normal conditions, gold atoms arrange themselves in what is known as a face-centered cubic (FCC) structure, where atoms sit at the corners of a cube and at the center of each cube face. This structure is known to be stable over a wide range of pressures, but models differ on when it begins to break down.
The new measurements show that the FCC structure persists to much higher pressures than some predictions suggested, up to about twice the pressure at Earth’s core.
Gold’s transition revealed
At still higher pressures, the researchers observed the first signs of a structural shift. Some atoms rearranged into a body-centered cubic (BCC) structure, in which atoms sit at each cube corner with one at the center.
Importantly, the original FCC pattern did not completely disappear. Instead, the results showed evidence of both structures coexisting under the most extreme compression achieved in the study.
The coexistence of phases provides a clearer view of how gold transitions between structures and underscores the importance of measuring temperature more precisely at these pressures. “These experiments extend structural measurements of gold into the terapascal regime and highlight the need for temperature diagnostics to refine phase boundaries,” Coleman highlighted.
Understanding these transitions has practical significance. Gold is widely used as a pressure calibrant because it is chemically stable and readily detectable by X-ray analysis. Its behavior at lower pressures is well understood, but discrepancies at extreme pressures have affected the accuracy of other experiments.
“Knowing precisely how gold behaves ensures that every other experiment using it as a calibrant, from studying planetary cores to designing new materials, is grounded in a robust and validated understanding of gold’s behavior,” Coleman added.
The results provide a stronger foundation for future high-pressure research, enhancing confidence in experiments probing the conditions in planetary interiors and in high-energy physics.
The study was published in Physical Review Letters.