Temperature Dependence of the Lattice Vibrations of Triglycine Sulfate

Far infrared spectra from 400 to 30 cm-1of triglycine sulfate and its deuterated analogue were measured and the bands due to the librational modes of glycine molecules were identified. Polarized Raman spectra below 300 cm-1of triglycine sulfate single crystals were measured and the symmetry species of the observed lattice vibrations were determined. Temperature dependence of the lattice vibrations was examined. Significant changes were detected in both infrared and Raman spectra on crossing the Curie temperature, indicating a flipping motion of glycine I in the paraelectric phase and suggesting the ferroelectric transition in triglycine sulfate to be of an order-disorder type.