Vibrational study of phase transitions in (C₃H₇NH₃)₂PbCl₄

Abstract

Abstract Infrared and Raman spectra (5–3500 cm −1 ) of polycrystalline samples of (C 3 H 7 NH 3 ) 2 PbCl 4 and of its deuterated derivative were investigated in the temperature range 90–300 K. An assignment of the observed bands at room temperature is proposed. A temperature dependence study of the frequencies, ν, and half‐widths, Δν 1/2 , of some low‐frequency Raman bands revealed two phase transitions at about 110 and 170 K, whereas the deuterated compound showed only one phase transition at about 150 K in the same temperature range. These transitions are believed to be governed by libration of the cation coupled with NH 3 group jumps between different potential wells. The value of activation energy, E 0 = 3.2 kJ mol −1 , was calculated from the plot of Δν 1/2 ν s. temperature; it is of the same order of magnitude as the potential barrier, V 6 = 3.53 kJ mol −1 , calculated from the torsional frequency of NH 3 + (288 cm −1 ).