Raman investigation of the order-disorder phase transitions in the 2[N(C3H7)4]SbCl4 compound

The Raman spectra of bis (tetrapropylammonium tetrachloroantimonate (III)) 2[(C3H7)4N]SbCl4 compound single crystals were studied in the wavenumber range from 3500 to 50 cm−1 for temperatures between 300 and 415 K. Two phase transitions occurring at 343 (Ttr1) and 363 K (Ttr2) were observed and characterized. The strong evolutions of the Raman shift, half-widths and intensity of many lines associated with the organic cations were observed with discontinuities in the vicinity of the two phase transitions. The most important changes were noticed for the band at 307 cm−1 (at room temperature) assignable to the torsion of CH3 groups of the cations. The spectral characteristics of this band was analyzed and consistently described in the framework of an order-disorder model for the two phase transitions. They allowed us to obtain information relative to the activation energy, the correlation length, and the critical exponent of the mechanism. The decrease of the estimated activation energies for the band 307 cm−1 with the increase in temperature has been interpreted in terms of a change in the reorientation motion of cations. The temperature dependence of the reduced peak intensity allowed for the determination of the critical exponents and evolution of the correlation length on approaching the transition.