Coupling between proton pseudo-spins and normal modes in ferroelectric glycinium phosphite

Abstract

This work reports a study of the temperature dependence 290–20 K of the lattice dynamics of glycinium phosphite obtained from polarized Raman spectroscopy X yy Z and infrared reflectivity E b measurements. The loss of the inversion center at the para-ferroelectric phase transition gives rise to the activation of additional infrared and Raman bands. The oscillator strength of some infrared lattice modes that arise in the ferroelectric phase can be correlated with the temperature dependence of the order parameter of the phase transition. Several anomalies, which have been detected in the temperature dependence of the frequency and of the damping coefficient of some external and internal modes of the phosphite group, are described by a theoretical model that takes into account the coupling between proton pseudo-spins and phonons. The results obtained indicate that the phosphite group behavior affects the characteristic time of the proton flipping motion and reflects the long range ferroelectric order in glycinium phosphite.