Neutron scattering studies on ionic diffusion behaviors of superionic α- Cu2−δ Se

Abstract

We present studies on crystal structure and ionic diffusion behaviors of superionic [Formula: see text] Se ( δ = 0, 0.04, and 0.2) by utilizing neutron powder diffraction and quasi-elastic neutron scattering. In the superionic phase, the structural model with Cu ions occupying the Wyckoff sites of 8 c and 32 f provides the best description of the structure. As the content of Cu increasing in [Formula: see text] Se, the Cu occupancy increases on the 32 f site but decreases on the 8 c site. Fitting to the quasi-elastic neutron scattering spectra reveals two diffusion modes: the localized diffusion between the 8 c and 32 f sites and the long-range diffusion between the adjacent 8 c sites using the 32 f site as a bypass. Between 430 and 650 K, we measured that the compound with more Cu content exhibits a larger long-range diffusion coefficient. Temperature in this range does not affect the long-range diffusion process obviously. Our results suggest the two diffusion modes cooperative and, thus, provide a microscopic understanding of the ionic diffusion of the Cu ions in superionic [Formula: see text] Se.