Xe(N2)2compound to 150 GPa: Reluctance to the formation of a xenon nitride

The $\mathrm{Xe}\text{\ensuremath{-}}{\mathrm{N}}₂$ binary phase diagram was determined at 296 K from the pressure evolution of 14 different concentrations. The properties of $\mathrm{Xe}\text{\ensuremath{-}}{\mathrm{N}}₂$ mixtures were characterized using visual observation, Raman spectroscopy, and powder x-ray diffraction. Above 4.9 GPa, the $\mathrm{Xe}({\mathrm{N}}₂{)}₂$ van der Waals compound is stable and adopts the $\mathrm{MgC}{\mathrm{u}}₂$-type Laves phase structure $(Fd\text{\ensuremath{-}}3m)$ with ${\mathrm{N}}₂$ molecules orientationally disordered. At 10 GPa, this cubic lattice undergoes a martensitic phase transition into a tetragonal $(I{4}₁/amd)$ unit cell. This transition is associated with a partial ordering of the ${\mathrm{N}}₂$ molecules, possibly due to the growing ${\mathrm{N}}₂\text{\ensuremath{-}}{\mathrm{N}}₂$ quadrupole-quadrupole interaction with density. No other phase transition was detected up to 154 GPa, even after heating the sample to 2000 K. Above 30 GPa, a softening of the ${\mathrm{N}}₂$ vibron mode with pressure reveals a weakening of the ${\mathrm{N}}₂$ intramolecular bond that suggests an electronic redistribution between ${\mathrm{N}}₂\text{\ensuremath{-}}{\mathrm{N}}₂$ and $\mathrm{Xe}\text{\ensuremath{-}}{\mathrm{N}}₂$ entities. These interactions could explain the great stability of the $\mathrm{Xe}({\mathrm{N}}₂{)}₂$ compound. However, no xenon nitride was observed.