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 similar to 6.5 and similar to 16.0 GPa, respectively. Upon compression, the shearing distortion of the unit cell induced the displacive structural transition of phase alpha -> gamma. Further analyses of the mid-IR spectra indicate the evolution of N-3(-) with the arrangement sequence of orthogonal -> parallel -> orthogonal during the phase transition of phase alpha -> gamma -> delta. Additionally, the pressure-induced nonlinear/asymmetric existence of N=N=N and the two crystallographically nonequivalent sites of N-3(-) were observed in phase delta.