VIBRATIONAL STUDY OF PHASE-TRANSITIONS IN (C3H7NH3)2PBCL4

Infrared and Raman spectra (5–3500 cm−1) of polycrystalline samples of (C3H7NH3)2PbCl4 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, Δν1/2, 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 NH3 group jumps between different potential wells. The value of activation energy, E0 = 3.2 kJ mol−1, was calculated from the plot of Δν1/2 νs. temperature; it is of the same order of magnitude as the potential barrier, V6 = 3.53 kJ mol−1, calculated from the torsional frequency of NH3+ (288 cm−1). Copyright © 1990 John Wiley & Sons, Ltd.