Ferroelectric-ferroelastic phase transition in β-LiNH4SO4:: NIR Raman and domain structure studies

Results of detailed temperature investigations of the ferroelastic domain structure and polarized NIR Raman spectra in the close vicinity of the ferroelectric-ferroelastic phase transition in beta-LAS are presented. Optical observations of (100) and (010) surfaces during cooling revealed the existence of an additional system of stripes besides ferroelastic domains, several degrees below the temperature of phase transition. The orientation of the stripes corresponds to the orientation of the phase front. A discontinuous anomaly of frequencies characteristic of the SO4 molecular group was observed at the phase transition temperature T-2.