Scientists at Stony Brook University have been able to show that the
element sodium (Na), becomes transparent when under
Sodium (left) is a white metal at lower pressures; turns black when pressure is increased (center); and turns red transparent at even higher pressures (right).
“It is well known that at sufficiently high compression all materials must go metallic,” said Artem Oganov, Professor of Theoretical Crystallography at Stony Brook University. “This is seen in the metallization of hydrogen at high pressures and temperatures inside planets Jupiter and Saturn.”
The researchers found that increasing pressure on the element sodium has results previously not known. While sodium is a perfectly white metal at normal pressure, increasing the pressure first turns the element black, then red transparent, and finally it becomes a colorless see-through material, similar to glass.
Yanming Ma, the lead author and professor of physics at Jilin University in China, was the first to predict this transformation. His calculations showed that sodium takes on unusual crystal structures and transforms to an insulator in high pressures.
“In these holes electrons demonstrate an extremely localized behavior, responsible for the collapse of the metallic state,” said Ma. “These electrons behave as ‘fake atoms,’ just like in electrides - ionic compounds where the role of the anion is played by localized electrons.”
In order to test out Ma’s calculations and theories, researchers conducted a series of very difficult experiments using tiny micrometer-size samples. They were able to confirm Ma’s predictions of the structure and transparency of sodium.
“What fascinated us most is that the pressures at which this transformation was predicted were experimentally reachable,” Oganov said, “and that at these conditions such a remarkable change of chemistry occurs”.
These findings were reported in the journal Nature.