Eur. Phys. J. B 40, 167-176 (2004)
https://doi.org/10.1140/epjb/e2004-00255-1

Two dimensional fluoride ion conductor RbSn₂F₅ studied by impedance spectroscopy and ¹⁹F, ¹¹⁹Sn, and ⁸⁷Rb NMR

¹ Department of Chemistry, Graduate School of Science, Hiroshima University, Kagamiyama 1-3-1, Higashi-Hiroshima 739-8526, Japan
² Institute for Materials Science, Darmstadt University of Technology, Petersenstrasse 23, 64287 Darmstadt, Germany

Corresponding author: ^a mmahmad@sci.hiroshima-u.ac.jp

Received: 4 April 2003
Revised: 25 May 2004
Published online: 12 August 2004

Abstract

RbSn₂F₅ is a two-dimensional fluoride ion conductor. It undergoes a first-order phase transition to a superionic state at 368 K. The structure of the low temperature phase has been determined from the Rietveld analysis of the X-ray powder diffraction. The dynamic properties of the fluoride ions in RbSn₂F₅ have been studied by impedance spectroscopy and solid state NMR. The dc ionic conductivity of this sample shows an abrupt increase at the phase transition temperature. We have obtained the hopping frequency and the concentration of the charge carriers (F^- ions) at different temperatures from the analysis of the conductivity spectra using Almond-West formalism. The estimated values of the charge carriers' concentration agree well with that determined from the structure and were found to be independent of temperature. The relatively small value of the power-law exponent, , supports the two-dimensional property of the investigated material. Furthermore, ¹⁹F NMR with simulation has suggested the diffusive motions of the fluoride ions between different sites. In contrast, ¹¹⁹Sn and ⁸⁷Rb NMR spectra below 250 K supported the intrinsic disordered nature due to the random distribution of the fluoride ion vacancies.