Cation and anion dynamics in the fast-ion conducting rotor phase of 7Li 2SO 4

Abstract

Quasielastic neutron scattering experiments have been performed on the high-temperature α phase of 7Li 2SO 4. Our aim was to examine both anion and cation dynamics and their possible correlation (“paddle–wheel mechanism”) in this material which is the most prominent example of a fast cation conducting plastic phase. At Q<1.2 A ̊ −1 , the quasielastic line width varies as DQ 2, where D represents the Li tracer diffusion coefficient. At higher Q, we find a wave-like structure with line width maxima at 1.4 and 2.5 A ̊ −1 and a minimum at 1.9 A ̊ −1 . This behavior is typical of coherent diffusion ( 7Li scatters both coherently and incoherently). We also see, at higher Q, a (coherent) quasielastic contribution from the oxygen nuclei due to anion reorientation.