Effect of pressure on sodium azide studied by spectroscopic method

The high-pressure Raman and IR measurements of NaN3 were performed at room temperature with pressure up to 35.0 and 26.0 GPa, respectively. Three phase transitions of β-NaN3 → α-NaN3 → γ-NaN3 → δ-NaN3 were revealed at 0.5, 14.0, and 27.6 GPa. All fundamental vibrational modes were analyzed based on experimental and theoretical methods. The phase transition from β-NaN3 to α-NaN3 is attributed to the shearing distortion of unit cell and the rotation of the azide ions with increasing pressure. The abnormal symmetric evolution of bending modes observed in IR measurements reveals the rotational behavior of azide groups upon compression. Moreover, the azide ions might evolve into an energetically favorable arrangement under a higher pressure.