Diamond Melts: Not Like Ice, But Weirder

Diamond, the hardest known natural mineral, has been observed to melt, though its behavior is far from ordinary. Physicists have recently conducted experiments that reveal diamond remains in its familiar cubic crystal lattice until the moment it liquefies, rather than transitioning into a predicted BC8 phase. This finding resolves a long-standing discrepancy between experimental results and quantum-mechanical predictions regarding diamond's melting temperature, with new measurements aligning closely with theoretical calculations.

These experiments, conducted under pressures up to 1.8 terapascals, showed that solid diamond is less dense than the molten carbon it forms. This counterintuitive property means diamond could float on a pool of liquid carbon, similar to how ice floats on water. Interestingly, at certain pressure ranges, increasing pressure actually lowers the melting point of diamond.

The research has significant implications for understanding the interiors of ice giant planets like Uranus and Neptune. Furthermore, improved knowledge of carbon behavior under extreme pressure enhances computer models for inertial confinement fusion experiments, potentially increasing energy gain predictions by up to threefold. The findings were published in Nature Physics.