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Study of Fluoride Ion Motions in PbSnF4 and BaSnF4 Compounds With Molecular Dynamics Simulation and Solid State NMR Techniques

Published online by Cambridge University Press:  18 March 2011

Santanu Chaudhuri ,
Michael Castiglione ,
Francis Wang ,
Mark Wilson ,
Paul A. Madden  and
Clare P. Grey
Santanu Chaudhuri
Affiliation:
SUNY Stony Brook, Dept. of Chemistry, New York, USA
Michael Castiglione
Affiliation:
Physical and Theoretical Chemistry Laboratory, University of Oxford, UK
Francis Wang
Affiliation:
SUNY Stony Brook, Dept. of Chemistry, New York, USA
Mark Wilson
Affiliation:
Physical and Theoretical Chemistry Laboratory, University of Oxford, UK
Paul A. Madden
Affiliation:
Physical and Theoretical Chemistry Laboratory, University of Oxford, UK
Clare P. Grey
Affiliation:
SUNY Stony Brook, Dept. of Chemistry, New York, USA
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Abstract

A combined approach, using solid state NMR and Molecular Dynamics (MD) simulations, has been employed in this work to investigate fluoride-ion motion in the PbSnF4 family of anionic conductors, materials that contain double layers of Sn2+ and M2+ cations. 19F MAS NMR spectra of PbSnF4 and BaSnF4 show that the fluoride ions are mobile on the NMR timescale (10−4 s), even at room temperature. In the case of BaSnF4, two different groups of fluoride ions were observed, one group corresponding to fluorine atoms between the layers of Ba2+ cations, and the other set, corresponding to mobile fluoride ions undergoing exchange between sites in the Ba-Sn and Sn-Sn layers. The 119Sn NMR suggests a highly distorted Sn environment in these compounds, consistent with the presence of stereoactive Sn lone pairs. MD simulations, using the Polarizable Ion Model, have been carried out to probe the conduction mechanism. These simulations are able to reproduce elements of the structure such as the reduction in the occupancy of the fluorine ions between the Sn-Sn layers. Anisotropic conductivity, involving primarily motion in the M-Sn layers, is predicted, consistent with the NMR results. In the case of BaSnF4, no motion involving the fluoride ions in the Ba-Ba layers is observed on the simulation timescale (10−12 s) and a cyclic mechanism of fluoride-ion motion involving two types of fluoride ions in the Ba-Sn layers is proposed.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 658: Symposium GG – Solid-State Chemistry of Inorganic Materials III , 2000 , GG10.9
Copyright
Copyright © Materials Research Society 2001

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References

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