Fig. 2.

Evolution of the Raman modes of the Mg₂N₄ compounds with pressure. a Typical Raman spectra of Mg₂N₄ taken during decompression from 53.5 GPa to ambient conditions. The spectra at ambient conditions is markedly different than those at higher pressures, evidencing a phase transition. b Pressure dependence of the Raman modes' frequencies, which evolve smoothly and continuously down to 2.3 GPa. Red dots indicate the modes at ambient pressure. The spectra are offset along the y-axis for clarity and ×5 indicates that the spectrum is five-times magnified