# FT-IR AND NQR STUDIES OF PHASE TRANSTION IN $\alpha-KIO_{3}$ CRYSTAL

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 Title: FT-IR AND NQR STUDIES OF PHASE TRANSTION IN $\alpha-KIO_{3}$ CRYSTAL Creators: Puchkovskaya, G.; Barabash, Alexander; Gavrilko, T.; Baran, J.; Ratajczak, H. Issue Date: 1995 Publisher: Ohio State University Abstract: Ferroelectric $\alpha-kIO_{3} \cdot HIO_{3} (T_{c} = 223k)$ at T = 300k belongs to monoclinic $syngony^{1}$ (space group $p21/c, z = 4$) and consists of two sets of dimers $H(Io3)2^{-}$, connected by strong $(R_{O\ldots O} = 2, 5A)$ hydrogen bonds. In order to clarify the structure of low-temperature ferroelectric phase and the dynamics of phase transition the temperature variable FT - IR study $(4000-400 cm^{-1})$ of polycrystalline $\alpha-KIO_{3} \cdot HIO_{3}$ have been performed from T = 300 to 13k. Pressure dependable NQR measurements (0 - 5kbar) have been performed $earlier^{2}$ at T=300 and 77K. On cooling to low temperatures the ABC structure of OH stretching vibrations $(1600 - 2800cm^{-1})$ slightly varies: the middle frequency band (B) shows the asymmetric contour and moves slightly to lower frequencies; the intensity of it decreases, whereas those of bands A, and particularly C, increase. Another striking feature in these spectra is a very strong absoraption culminating between 600 and $1200cm^{-1}$ which shows a doublet structure on cooling. Such spectral distribution is typical for symmetrical strong H-bonds between two equivalent molecules related by a center of inversion or a two-fold axis. These facts correlate well with structural $data^{1}$ and confirm the NQR conclusions about distortion of anion sublattice along with the crystal space group lowering to $P2_{1}$ at the phase transition temperature. Description: 1. A. Petrosyan, A. Busch, V. Chechkin, V. Volkov, Yu. Venevtsev, Ferroelectrics, 21, 525 (1978) 2. A. Barabash, D. Baisa, E. Shadchin, Khimilcheskaya Fizika (in Russian), 5, 1506 (1986). Author Institution: National Academy of Sciences of Ukaraine, 46 Nauki Prosp., 252650 Kiev, Ukraine; Polish Academy of Sciences, 50-950 Wroclaw 2, P.O. Box 937, Poland URI: http://hdl.handle.net/1811/29952 Other Identifiers: 1995-FE-07