NEUTRON-SCATTERING BY SUPERIONIC CONDUCTOR GLASSES

Small angle, quasi-elastic and inelastic neutron scattering experiments on various superionic conductor glasses are analyzed. In the AgPO3 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 0.65AgPO3-0.35AgBr and those of the 0.5AgPO3-0.5AgI glass indicates the existence of AgBr4 clusters dispersed in the AgPO3 matrix. The same result is found in the fast ionic conductor glass 0.85AgPO3-0.15PbI2: this implies an exchange between Ag+ and Pb2+. The cluster radius of 20 angstrom in that case is much larger than for AgPO3-AgI glasses where the radii of gyration are of the order of 4 angstrom only. The diffusion of Cu+ has been studied in the fast ionic conductor 0.5CuPO3-0.5CuI. 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 alpha-CuI rich phase and that the observed Cu+ motion is very short-range, and does not contribute to the ionic conductivity.