Nitrogen, a seemingly simple diatomic element, boasts a complex phase diagram with 16 solid phases, making it pivotal for solid-state science theories. At ambient pressure and temperature, nitrogen is a gas and is found in the form of an N₂ molecule (N≡N) composed of an extremely strong triple-bond. Under extreme pressures of 2.54 GPa (i.e. 25,400 atmospheres), nitrogen becomes solid. Upon further pressure increase to 80 GPa, nitrogen undergoes a progressive transformation from molecular solid to a three-dimensional network of single-bonded atoms.

The elusive ζ-N₂ phase, existing between 60 and 115 GPa, holds the key to understanding this transition. Using diamond anvil cells, molecular nitrogen was compressed to pressures between 63 and 80 GPa and laser heated to recrystallize submicrometer ζ-N₂ crystallites. Single-crystal X-ray diffraction experiments were conducted at the PETRA III and the ESRF synchrotrons and, from the obtained data was obtained a full structure model.

In this talk, we will describe the hitherto unknown structure of ζ-N₂ and its implications for the transformation of molecular nitrogen into an amorphous, single-bonded solid. In particular, density functional theory (DFT) calculations reveal a gradual shift of electron density, forming electronic bridges at 130 GPa and a 1D percolation at 150 GPa, providing a possible explanation for the formation of the single-bonded amorphous nitrogen.


 

high temperature and high pressure,synchrotron x-ray diffraction,molecular nitrogen,simple molecular systems