Raman study of order-disorder phase transition in [(C3H7)4N]3Bi3Cl12 compound

The [(C3H7)4N]3Bi3Cl12 compound that crystallizes at room temperature in a centrosymmetric triclinic system (P1¯ space group) is studied on heating up to its melting temperature. Differential scanning calorimetry investigations disclosed an irreversible phase transition at T = 414 K. Raman scattering studies (140-3500 cm−1) were investigated in the temperature range 398-438 K. A detailed analysis of the frequency, half-width and reduced intensity of the bands associated to υ(Bi-Cl) (at 254 cm−1), υ(Bi-Cl) (at 287 cm−1) and υs(N-C-C)+δs(C-N-C) (at 1034 cm−1) is quantitatively described in term of an order-disorder phase transitions. The temperature dependence of the correlation lengths of these three bands is consistent with a disordered state at high temperature. This behavior is presumably governed by the reorientational motion of the alkylammonium chains of the cations between two sites coupled with changes of interactions with the anionic groups.