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# A Study of Superionic $CsHSO_4$ and $Cs_{1-x}Li_xHSO_4$ by Vibrational Spectroscopy and X-Ray Diffraction

Varma, Vijay and Rangavittal, N and Rao, CNR (1993) A Study of Superionic $CsHSO_4$ and $Cs_{1-x}Li_xHSO_4$ by Vibrational Spectroscopy and X-Ray Diffraction. In: Journal of Solid State Chemistry, 106 (1). pp. 164-173.

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## Abstract

Infrared and Raman spectroscopic studies of CsHSO4 suggest the occurrence of the following phase transitions: $IV\rightleftharpoons_{340K}III\rightleftharpoons_{380K}II\rightleftharpoons_{417K}I$. While the ordered phase, IV, has a monoclinic structure, the high-temperature superionic phase, I, has a tetragonal structure involving the free rotation of $HSO_4^-$. Phase II is close to being orthorhombic with a small monoclinic distortion. The transition to the superionic phase, I, is accompanied by the appearance of broad, structureless bands in the infrared and Raman spectra, as well as changes in the $O-H$ stretching region due to decrease in hydrogen bonding. Accompanying the III-II transition, we observe the disappearance of the $O \cdots O$ stretching and $\delta(S-OH)$ bands and a decrease in the $HSO_4^-$ libration frequency. Across the phase transitions, the separation between the v(S-O) and v(S-OH) bands shows stepwise changes. The high-temperature superionic phase essentially has sulfate-like species with a relatively short S-O bond, in contrast to the low-temperature phase, which has long and short S-O distances. Substitution of Cs by Li in $CsHSO_4$ has an effect similar to that of increasing the temperature. The vibrational spectrum of $Cs_{0.7}Li_{0.3}HSO_4$ corresponds to a state of disorder between those of phases II and I.

Item Type: Journal Article Copyright of this article belongs to Elsevier. Division of Chemical Sciences > Solid State & Structural Chemistry Unit 29 Jun 2006 19 Sep 2010 04:29 http://eprints.iisc.ernet.in/id/eprint/7737

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