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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 February 2011

D. Wilmer ,
H. Feldmann ,
R.E. Lechner  and
J. Combet
D. Wilmer
Affiliation:
Münster University, Institute of Physical Chemistry and Sonderforschungsbereich 458, Schlossplatz 4/7, 48149 Münster, Germany
H. Feldmann
Affiliation:
Münster University, Institute of Physical Chemistry and Sonderforschungsbereich 458, Schlossplatz 4/7, 48149 Münster, Germany
R.E. Lechner
Affiliation:
Hahn-Meitner-Institut, Glienicker Str. 100, 14109 Berlin, Germany
J. Combet
Affiliation:
Institut Laue-Langevin, 6 rue Jules Horowitz, 38042 Grenoble Cedex 9, France
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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 FWHM (thereby shifting the dynamic window to the nanosecond scale) allowed to examine sodium diffusion in x Na2SO4 · (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.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 835: Symposium K – Solid-State Ionics , 2004 , K1.2
Copyright
Copyright © Materials Research Society 2005

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