A Raman scattering investigation of the pressure-induced phase transition in tetragonal thallium azide (TlN3) is reported. The most interesting features of the Raman spectrum of TlN3 are the anti-resonant line-shapes of two Eg symmetry phonons at 35 and 50 cm-1 superimposed on a quasi-elastic wing. The scattering data is shown to be consistent with a model in which the two phonons interact via an imaginary coupling term. The phonon at 35 cm-1 (assigned to a translational shear mode of the Tl+ sublattice) softens with increasing pressure and increases in linewidth as P approaches P0 (=8 kbar) from below. At the same time, the quasi-elastic scattering component (associated with large amplitude N3- librational fluctuations) becomes less damped. A displacive structural transition from tetragonal to monoclinic is indicated by the eigenvector of the soft phonon.
All Science Journal Classification (ASJC) codes
- Materials Science(all)
- Condensed Matter Physics