High-Pressure Studies of Rubidium Azide by Raman and Infrared Spectroscopies

We report the high-pressure studies of RbN3 by Raman and IR spectral measurements at room temperature with the pressure up to 28.5 and 30.2 GPa, respectively. All the fundamental vibrational modes were resolved by combination of experiment and calculation. Detailed spectroscopic analyses reveal two phase transitions at ∼6.5 and ∼16.0 GPa, respectively. Upon compression, the shearing distortion of the unit cell induced the displacive structural transition of phase α → γ. Further analyses of the mid-IR spectra indicate the evolution of N3– with the arrangement sequence of orthogonal → parallel → orthogonal during the phase transition of phase α → γ → δ. Additionally, the pressure-induced nonlinear/asymmetric existence of N═N═N and the two crystallographically nonequivalent sites of N3– were observed in phase δ.