Physicists discover unexpected diamond melting behavior under extreme pressure

Physicists led by Marius Milo from the Lawrence Livermore National Laboratory have conducted experiments melting diamonds under extreme conditions, including temperatures exceeding the surface of the Sun and pressures between 600 gigapascals and 1.8 terapascals. These conditions mimic the interiors of ice giants like Uranus and Neptune.

Contrary to previous theoretical models, the diamond did not transition into the predicted BC8 carbon phase before melting. Instead, researchers observed that the diamond maintains its known cubic crystal structure right up until the moment it melts into a disordered state. This unexpected behavior suggests the material remains ‘trapped’ in its diamond structure because it lacks the time to undergo a phase change when exposed to a single shock wave.

Using the OMEGA laser facility at the University of Rochester, the team monitored temperature, pressure, and atomic structure via X-ray. The melting temperature at one terapascals was measured at approximately 7,300 Kelvin, aligning more closely with theoretical predictions than previous experimental estimates. These findings may assist in the study of planetary interiors and the improvement of nuclear fusion experiments.