FAST IONIC-DIFFUSION IN LI2S INVESTIGATED BY QUASI-ELASTIC NEUTRON-SCATTERING

The Li diffusion in Li2S at high temperatures was investigated by quas ielastic neutron scattering techniques on a single crystal of (Li2S)-L i-7. It is shown by using polarized neutrons that the scattering is al most purely incoherent. The data were analysed in terms of an extended Chudley-Elliott jump diffusion model. The Li diffusion process takes place by hopping between regular tetrahedral and interstitial octahedr al sites. The mean residence times on the regular Li sites were estima ted to be 17.3 ps at T = 1173 K, 6.7 ps at 1273 K and 4.3 ps at 1363 K .