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Vibrational study on ferroelectric phase transition in NaNH4SO4 · 2H2O

✍ Scribed by Isao Kanesaka; Kenichi Ozaki

Publisher
John Wiley and Sons
Year
1994
Tongue
English
Weight
351 KB
Volume
25
Category
Article
ISSN
0377-0486

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✦ Synopsis

Abstract

The vibrational spectra of NaNH~4~SO~4~ · 2H~2~O (SASD) and its 5% deuterated system were observed in the region of the O–X and N–X stretches (X = H or D) over the temperature range 300–25 K. A similarity was found in the Raman spectral features associated with water molecules at room temperature and below T~c~, which were, however, different from those just above T~c~. A λ type of temperature dependence with a large wavenumber jump at T~c~ was found for the main Raman band at 3423 cm^−1^. This was explained qualitatively in terms of the strong correlation between the Raman mode and the order parameter. A similar result was observed for the decoupled OD modes. The analysis of their temperature dependence revealed characteristics of the phase transition mechanism in SASD. The λ type of temperature dependence was not found in decoupled modes associated with ammonium ions.

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