Using super-high pressures Washington State University researchers have created a compact, never-before-seen material capable of storing vast amounts of energy. It is the most condensed form of energy storage outside of nuclear energy.
The researchers increased the pressure to more than a million atmospheres and forced the molecules to make tightly bound three-dimensional metallic “network structures.” In the process, the huge amount of mechanical energy of compression was stored as chemical energy in the molecules’ bonds.
The application of pressure, internal or external, transforms molecular solids into extended solids with more itinerant electrons to soften repulsive interatomic interactions in a tight space. Examples include insulator-to-metal transitions in O2, Xe and I2, as well as molecular-to-non-molecular transitions in CO2 and N2. Here, we present new discoveries of novel two- and three-dimensional extended non-molecular phases of solid XeF2 and their metallization. At ∼50 GPa, the transparent linear insulating XeF2 transforms into a reddish two-dimensional graphite-like hexagonal layered structure of semiconducting XeF4. Above 70 GPa, it further transforms into a black three-dimensional fluorite-like structure of the first observed metallic XeF8 polyhedron. These simultaneously occurring molecular-to-non-molecular and insulator-to-metal transitions of XeF2 arise from the pressure-induced delocalization of non-bonded lone-pair electrons to sp3d2 hybridization in two-dimensional XeF4 and to p3d5 in three-dimensional XeF8 through the chemical bonding of all eight valence electrons in Xe and, thereby, fulfilling the octet rule at high pressures.