Polarized Raman spectra of [N(CH3)4]2ZnCl4 crystals are studied in phase I in the frequency range between 10 and 3500 cm−1. An assignment of the lines observed to motion types is carried out. The sublattice of the TMA ions is found to behave as a quasi‐liquid. The distorsion of the ZnCl 42‐ tetrahedra is insignificant. A considerable orientational disorder is shown to occur in this phase.

Yu. I. DURXEV et al.: Vibrational Spectra and Phase Transitions (I)

The polarized Raman spectra of recently synthesized [N(CH3)4]2ZnCl4 and [(CH3)2NH2]2CoCl4 crystals are obtained. The structure of these spectra exhibits strong similarities with that of [N(CH3)4]2ZnCl4. The vibration spectra of these crystals at room temperature are analyzed and the similarity of the spectra with those of the ordered low‐symmetry phase (176–155 K) of the [N(CH3)4]2ZnCl4 crystal is discussed.

Low-frequency (v < 50 cm-') polarized Raman spectra of TMATC-Zn crystals are studied in the temperature range between 300 and 100 K that covers the range in which the structural phase transitions of this compound occur. The appearance of lines with frequencies below 17cm-' is observed in commensurately modulated low-symmetry phases. These lines correspond to the phonons of transverse acoustic branches in the T-C-X direction of the normal phase which transfer to the zone center as a result of the unit cell multiplication. A sharp drop in the relaxational contribution to the scattering spectrum is found for frequencies below 20 cm-' in phases V and V1 which is thought to be associated with ordering processes in the crystal lattice. Polarisierte, niederfrequente (v < 50 cm-I) Ramanspektren von TMATC-Zn-Kristallen werden imTemperaturbereich zwischen 300 und 100K untersucht, der den Bereich uberdeckt, in dem die strukturellen Phasenubergange dieser Verbindung auftreten. Das Erscheinen von Linien mit Frequenzen unterhalb 17 cm-' wird in kommensurabel modulierten Niedersymmetriephasen beobachtet. Diese Linien entsprechen den Phononen der transversalen akustischen Zweige in der T-C-X-Richtung der normalen Phase, die zum Zonenzentrum als Ergebnis der Einheitszellenmultiplikation ubergehen. Ein scharfer Abfall der Relaxationsbeitrage zum Streuspektrum wird fur Frequenzen unterhalb 20 cm-' in den Phasen V und VI gefunden, von denen angenommen wird, da13 sie mit Ordnungsprozessen im Kristallgitter verknupft sind.

Polarized Raman spectra of [N(CH3)4]2ZnCl4 single crystals are studied in five low‐symmetry phases in the frequency range 10 cm−1 < ν < 3500 cm−1. The observed lines are assigned on the basis of a factor‐group analysis and corresponding correlational relationships. The order of the crystal lattice is increased as the temperature is lowered. The phase transition in this compound are of order–disorder type.