High-pressure spectroscopic study of silver azide
The pressure-induced structural phase transition in AgN3 was investigated using Raman and infrared spectroscopy. At ambient pressure, the Raman-active bending and asymmetric stretch modes of NNN indicate the N3− is nonlinear and/or asymmetrical. Upon compression, a reversible orthorhombic-to-tetragonal phase transition was observed at ∼2.7 GPa, while the degeneration of the lattice modes was present due to the increasing symmetrical element. The softening of the v2(B2u) mode and hardening of the v2(B3u) mode demonstrate the rotation of the N3− during the phase transition, which reveals the essential source of the a-axis expansion and the structural phase transition. The perpendicular arrangement of N3− in the tetragonal structure is energetically favorable and beneficial for structural stability.