Hexagonal Layered Polymeric Nitrogen Phase Synthesized near 250 GPa

Area of Science:

• Materials Science
• High-Pressure Physics
• Solid-State Chemistry

Background:

• Nitrogen's triple bond dissociates around 100 GPa, leading to predicted polymeric structures.
• Previous studies reported cubic-gauche (cg-N) and mixed phases at high pressures and temperatures.

Purpose of the Study:

• To investigate the crystalline phases of pure nitrogen at ultra-high pressures.
• To characterize the structure of nitrogen above 240 GPa.
• To computationally assess the stability of observed nitrogen phases.

Main Methods:

• Laser heating of pure nitrogen at pressures from 180 GPa.
• X-ray diffraction and Raman spectroscopy for structural characterization.
• Density-functional theory calculations including thermal and dispersive effects.

Main Results:

• A sole crystalline phase, hexagonal layered polymeric nitrogen (HLP-N), was identified above 240 GPa.
• An amorphous transparent phase was observed below 240 GPa.
• X-ray diffraction confirmed a tetragonal lattice (P42bc) consistent with HLP-N.

Conclusions:

• The study identified and characterized a novel hexagonal layered polymeric nitrogen structure at ultra-high pressures.
• Computational analysis supports the stability of the HLP-N structure under these extreme conditions.
• This work expands the known phase diagram of nitrogen at gigapascal and terapascal pressures.