Determination of nitrogen's phase diagram up to 400 GPa

As an archetypal diatomic molecule, the high-pressure polymorphs of molecular nitrogen are an excellent testbed for refining solid-state physics models. Above 110 GPa, the physicochemical properties of nitrogen radically change as it transforms into a polymeric single-bonded solid. It exhibits unique characteristics, such as the highest chemical energy storage and ultra-stiff bonds, compelling for the design of novel functional materials. This proposal aims to uncover nitrogen's phase diagram between 180 and 400 GPa, discover novel polymeric phases and solve their structure with single-crystal X-ray diffraction from polycrystalline samples (SC-XRDp). These experiments will challenge current theoretical models and unveil novel forms of polynitrogen arrangements, providing a rare, but crucial, example of the behavior of simple homoatomic systems at ultrahigh pressures.