Synthesis of Polymeric Nitrogen

We report on an allotropic form of nitrogen where the atoms are connected with single covalent bonds, similar to carbon atoms in diamond. Nitrogen under ambient conditions consists of molecules where two atoms are strongly triple-bonded. The new substance was synthesized directly from molecular nitrogen at temperatures above 2,000 K and pressure above 110 GPa (ca. 1.1 million atmospheres) using a laser-heated diamond cell. From X-ray and Raman scattering we have identified this as the long-sought-after polymeric nitrogen with the theoretically predicted cubic gauche structure (cg-N). This cubic phase has not been observed previously in any element. The new phase is a stiff substance with bulk modulus ≥300 GPa, characteristic of strong covalent solids. This polymeric nitrogen is metastable, and contrasts with previously reported amorphous non-molecular nitrogen, which most likely is a mixture of small clusters of non-molecular phases. The cg-N represents a new class of single-bonded nitrogen materials with unique properties such as energy capacity: more than 5 times that of the energetically most powerful materials.