Neutron scattering by superionic conductor glasses

Abstract

Small angle, quasi-elastic and inelastic neutron scattering experiments on various superionic conductor glasses are analyzed. In the AgPO 3 based glasses, it is found that small clusters of AgI with tetrahedral coordination are dispersed in the matrix. The quasi-elastic signals originate from the diffusive motion of Ag =+ inside these clusters. The similarity between the quasi-elastic and inelastic spectra of the glass 0.65AgPO 3-0.35AgBr and those of the 0.5AgPO 3-0.5AgI glass indicates the existence of AgBr 4 clusters dispersed in the AgPO 3 matrix. The same result is found in the fast ionic conductor glass 0.85AgPO 3-0.15PbI 2: this implies an exchange between Ag + and Pb 2+. The cluster radius of 20 Å in that case is much larger than for AgPO 3-AgI glasses where the radii of gyration are of the order of 4 Å only. The diffusion of Cu + has been studied in the fast ionic conductor 0.5CuPO 3-0.5CuI. Only 22% of Cu + ions are implied in the diffusive motion which is observed by quasi-elastic scattering. This motion is much faster than in the Ag + glasses and its activation energy much lower. On the other hand, the measured conductivity is about the same. It seems that there are no clusters of α-CuI rich phase and that the observed Cu + motion is very short-range, and does not contribute to the ionic conductivity.