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Order‐disorder phase transition in diethylenetriammonium chlorocadmate single crystals determined by Raman spectroscopy
Author(s) -
Jebari F.,
Becker P.,
CarabatosNédelec C.
Publication year - 1994
Publication title -
journal of raman spectroscopy
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.748
H-Index - 110
eISSN - 1097-4555
pISSN - 0377-0486
DOI - 10.1002/jrs.1250250404
Subject(s) - raman spectroscopy , phase transition , spectroscopy , materials science , phase (matter) , order (exchange) , crystallography , analytical chemistry (journal) , chemistry , condensed matter physics , physics , optics , quantum mechanics , chromatography , organic chemistry , finance , economics
The Raman spectra of diethylenetriammonium chlorocadmate [(denH 3 )CdCl 5 ] single crystals were studied in the Raman shift range from 250 to 500 cm −1 for temperatures between 10 and 428 K. A phase transition at T c = 168 K was observed and characterized. In particular, two Raman bands were sensitive to temperature; they correspond to the torsion motions of NH 3 + at 353 cm −1 and to the skeleton deformations of the (denH 3 ) 3+ cations at 336 cm −1 to which NH 3 + belongs. The analysis of the NH 3 + torsion mode based on an order‐disorder model allowed the determination of the activation energy U (300 K) = 0.91 kcal mol −1 The assumption of cluster fluctuations also allowed the critical exponents to be obtained for the transition δ = 0.71 and β = 0.35, the orientation correlation time τ c = 0.5 × 10 −12 s at 300 K and the correlation length ζ 0 ≈ 13 b , b being the lattice parameter. It is concluded that the skeleton deformation mode is a localized excitation coupled to jumps of the torsion mode of NH 3 + .