Raman and infrared study of ferroelectric thiourea and rochelle salt

Abstract
We have observed the optical phonon modes in thiourea and Rochelle salt single crystals by means of polarized Raman and infrared spectroscopy. The spectra were recorded at several temperatures especially near the various phase transition points which are known to exist in both materials. The intention was to search for characteristic changes in the spectra near the transition temperatures. The observed frequency shifts and anomalous line broadening can be interpreted within the framework of a generalized pseudospin-phonon interaction first developped for the TGS-family1. We also discuss the observed intensity changes by applying a group theoretical method developped by Petzelt and Dvorak2.