Cation and anion dynamics in the fast-ion conducting rotor phase of (Li2SO4)-Li-7

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.