Disodium helide[2] (Na2He) is a compound of helium and sodium that is stable at high pressures above 113 gigapascals (1,130,000 bar).

Compared with other binary compounds of other elements and helium, it was predicted to be stable at the lowest pressure of any such combination.

This also means, for example, that a helium-potassium compound is predicted to require much higher pressures of the order of terapascals.

The material was synthesized by putting tiny plates of sodium in a diamond anvil cell along with helium at 1600 bar and then compressing to 130 GPa and heating to 1,500 K with a laser.

Energy is compensated by the relative shrinking of the helium atoms and the space for electrons.