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Sodium Ion Conduction in Plastic Phases: Dynamic Coupling of Cations and Anions in the Picosecond Range

Published online by Cambridge University Press:  01 August 2005

D. Wilmer ,
H. Feldmann ,
R.E. Lechner  and
J. Combet
D. Wilmer*
Affiliation:
Münster University, Institute of Physical Chemistry and Sonderforschungsbereich 458, 48149 Münster, Germany
H. Feldmann
Affiliation:
Münster University, Institute of Physical Chemistry and Sonderforschungsbereich 458, 48149 Münster, Germany
R.E. Lechner
Affiliation:
Hahn-Meitner-Institut, 14109 Berlin, Germany
J. Combet
Affiliation:
Institut Laue-Langevin, 38042 Grenoble Cedex 9, France
*
a) Address all correspondence to this author. e-mail: [email protected] This paper was selected as the Outstanding Meeting Paper for the 2004 MRS Fall Meeting Symposium K Proceedings, Vol. 835.
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Abstract

Results of simple computer simulations and model calculations for ion conducting rotor phases are compared to quasi-elastic neutron scattering data from solid solutions of sodium orthophosphate and sodium sulphate, xNa2SO4⋅(1 − x)Na3PO4. These materials are not only sodium fast-ion conductors in their high-temperature cubic phases but also show considerable dynamic reorientation disorder of their tetrahedral anions. At an elastic energy resolution of about 100 μeV, neutron spectrometry monitored oxygen scattering due to anion reorientation which occurs on the picosecond time scale. This thermally activated process exhibits activation energies between 0.184 eV (x = 0.0) and 0.052 eV (x = 0.5). Analysis of the quasielastic intensities as a function of scattering vector Q gives clear evidence of the involvement of cations in the anion reorientation. Increasing the elastic resolution to about 1 μeV full width at half-measure (FWHM) (thereby shifting the dynamic window to the nanosecond scale) allowed examination of sodium diffusion in xNa2SO4⋅(1 − x)Na3PO4. This process consists predominantly of thermally activated jumps between tetrahedrally coordinated sites, the activation energies ranging from 0.64 eV for x = 0.0 to 0.30 eV for x = 0.5.

Keywords

DiffusionIonic conductorNeutron scattering
Type
Outstanding Meeting Paper
Information
Journal of Materials Research , Volume 20 , Issue 8 , August 2005 , pp. 1973 - 1978
Copyright
Copyright © Materials Research Society 2005

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References

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