Quasielastic neutron scattering experiments have been performed on the high
-temperature alpha phase of (Li2SO4)-Li-7. Our aim was to examine bath anio
n and cation dynamics and their possible correlation ("paddle-wheel mechani
sm") in this material which is the most prominent example of a fast cation
conducting plastic phase. At Q < 1.2 Angstrom(-1), the quasielastic line wi
dth varies as DQ(2), where D represents the Li tracer diffusion coefficient
. At higher Q, me find a wave-like structure with line width maxima at 1.4
and 2.5 Angstrom(-1) and a minimum at 1.9 Angstrom(-1). This behavior is ty
pical of coherent diffusion (Li-7 scatters both coherently and incoherently
). We also see, at higher Q, a (coherent) quasielastic contribution from th
e oxygen nuclei due to anion reorientation. (C) 2000 Elsevier Science B.V.
All rights reserved.