A Raman scattering study of the pressure induced phase transition in s-triazine

Abstract

The pressure induced phase transition in s-triazine has been studied using Raman scattering. Some of the features observed in a previous Raman scattering study of the phase transition at atmospheric pressure have also been observed in the present case, and a preliminary analysis based on an estimated form of the pressure dependence of the order parameter is reported. However, the data presented in the present study can not yet be fully reconciled with the corresponding results at atmospheric pressure. It is suggested that some of the different theoretical ideas concerning the transition developed for atmospheric pressure and variable temperature could be applied in the analysis of the effects of pressure. No additional phases of s-triazine were observed at pressures up to about 30 kbar within the temperature range 15–295 K.

Pressure dependence of the Raman frequency shifts related to the thermodynamic quantities in phase II of s-triazine

“…In this study, we first analyzed the observed Raman frequencies of mode II [10] by using a polynomial a a P a P 2…”

“…As pointed out previously [10], the low-frequency E g mode in phase I (T<T c ) splits into the Raman bands I and II in phase II (T<T c ). The Raman band III is due to the molecular motions, which is observable in phase II (T<T c ) only [17].…”

“…It has been reported [10] that apart from the phases I and II, no additional phases of s-triazine have been observed at pressures up to about 30 kbar within the temperature range 15-295 K.…”

“…The I-II phase change has been obtained experimentally by nuclear quadrupole resonance [8] and neutron diffraction [9], as also shown in a P-T phase diagram of striaizine [10]. It has been reported [10] that apart from the phases I and II, no additional phases of s-triazine have been observed at pressures up to about 30 kbar within the temperature range 15-295 K.…”

“…Raman spectra of s-triazine have shown the bands I, II, III, IV and V for the temperature-induced [17] and the pressure-induced [10] I-II phase transition in this molecular crystal. As pointed out previously [10], the low-frequency E g mode in phase I (T<T c ) splits into the Raman bands I and II in phase II (T<T c ).…”