Successive phase transitions in tetramethylammonium tetrachlorozincate

$Me_4N)_2ZnCl_4 (TmAZnCl_4)$ shows 6 successive phase transitions at 80-300 K. Polarized Raman spectra of oriented single crystals of $TMAZnCl_4$ and the IR spectra by the $KBr$ pellet technique were recorded at 130-298 K, covering all the known phase transitions,. The frequency of the $Zn-Cl$ stretching vibration increases in Raman and IR spectra with decreasing temp. Three bands are found in the Raman spectrum in the region where Me frequencies usually occur and, in a similar way, 3 bands appear in the IR spectrum at low temp. due to the deformation vibrations of the Me group. The triggering mechanism of the phase transition at low temp. can be due to a coupling of the distortion of $ZnCl_{42}$- groups and the Me deformation, where the motion of relatively free Me rotations is slowed down, favoring 1 equilibrium position below 161 K. The phase transition appears to be an order-disorder one with Me rotational disorder in the high temperature paraelectric phase