TEMPERATURE VARIABLE LOW-FREQUENCY RAMAN SPECTRA AND ORIENTATION DISORDER IN $NH_{4}IO_{3}$ CRYSTAL
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Date
1995
Journal Title
Journal ISSN
Volume Title
Publisher
Ohio State University
Abstract
The ammonium iodate $NH_{4}IO_{3}$ crystal is $known^{1}$ as ferroelectric with displacing type phase transition $(T_{c} = 367K)$, Polarized temperature variable lowfrequency Raman scattering $(W < 200 cm^{-1})$ studies in the phase transition region are presented. Measurements of peak positions of ``external'' rotational and translation optical modes and their half-widths allow to detect the orientation disorder and help to determine its character as well as a mechanism of the phase transition to the ordered phase. It appeared to be continuous and of the mixed displacing and order-disorder character. Quantitative analysis of the spectra according to lattice dynamics theories and using $^{127}I$ NQR $analysis^{2}$ have been performed. Previous literature data are reviewed and the apparent discrepancies concerning the transition processes are elucidated on the basis of the present results.
Description
1. D. F. Baisa, A. I. Barabash, E.A. Shadcin, Fisika Tverdogo Tela (in Russian), 27, 2357 (1985). 2. A.I. Barabash, J. Mol. Struct., 210, 517 (1992).
Author Institution: National Academy of Sciences of Ukraine, Prosp. Nauki, 46, 252650 Kiev, Ukraine.
Author Institution: National Academy of Sciences of Ukraine, Prosp. Nauki, 46, 252650 Kiev, Ukraine.