Raman Spectra of [N(CH 3 ) 4 ] 2 ZnCl 4 Single Crystals I. Raman Spectra of the Parent Phase

et al. 1991

Self Cite

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.

“…The experimental technique is the same as in [3,41. The following lattice parameters were X-ray determined for our sample: a = 1.2268, b = 0.8946, and c = 1.5515 nm.…”

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Raman Spectra of [N(CH₃)₄]₂ZnCl₄ Single Crystals. III. Activation of Acoustic Phonons in Raman Spectra of the Commensurately Modulated Phases

Torgashev

et al. 1991

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“…In view of this fact, a comparison makes sense only between the spectra of low-symmetry phases and the spectra of phase 1. In Part I of this work the identification of Raman lines has been carried out [20]. We shall use hereafter the corresponding notation.…”

Section: Resultsmentioning

confidence: 99%

“…1. DURNEV Table 1 Phases, phase transition temperatures, space groups, and superstructure wave vectors of TMATC-Zn In Part I of this work [20], we have discussed in detail the Raman spectra of TMACT-Zn in the parent phase (Pnma). The present paper deals mainly with the spectra of the low-temperature phases.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Raman Spectra of [N(CH₃)₄]₂ZnCl₄ Single Crystals. II. Raman Spectra of Low‐Symmetry Phases

Торгашев

et al. 1991

Self Cite

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.

Raman Spectra of [N(CH₃)₄]₂ZnCl₄ Single Crystals IV. Isomorphous Substitutions. Raman Spectra of [(CH₃)₂NH₂]₂ZnCl₄ and [(CH₃)₂NH₂]₂CoCl₄ Crystals

Torgashev

et al. 1991

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.