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A study of the internal frequency region (400–4000 cm −1 ) of the Raman spectrum of a single crystal of sodium ammonium sulphate dihydrate, NaNH 4 SO 4 ·2H 2 O over the temperature range 293–87K
Author(s) -
Fawcett V.,
Long D. A.,
Sankaranarayanan V. N.
Publication year - 1975
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.1250030211
Subject(s) - raman spectroscopy , ion , phase transition , chemistry , single crystal , analytical chemistry (journal) , ferroelectricity , nuclear magnetic resonance , spectral line , sodium , lattice (music) , crystal (programming language) , crystallography , atmospheric temperature range , phase (matter) , crystal structure , dielectric , materials science , condensed matter physics , optics , physics , programming language , optoelectronics , organic chemistry , chromatography , astronomy , computer science , meteorology , acoustics
The Raman spectra in the region 400–4000 cm −1 of single crystals of NaNH 4 SO 4 ·2H 2 O in various orientations are reported for the temperature range 293–87K. NaNH 4 SO 4 ·2H 2 O undergoes a transition at 101 K from a paraelectric phase to a ferroelectric phase. The changes in the Raman spectra of the constituent species, NH 4 + , SO 4 2−and H 2 O as the temperature is lowered indicate that below the phase transition there are non‐equivalent ions in the unit cell. The abruptness of the spectral changes at 101 K suggests a large lattice distortion in accord with the predictions of magnetic resonance studies.