Brillouin scattering and neutron diffraction in ion-conducting glasses

We have performed neutron and Brillouin scattering studies of ion conducting (MX)x-(M2O-nB2O3)1-x glasses (MX≡LiCl, AgI). Neutron small-angle scattering experiments show no significant scattering from inhomogeneities of dimensions 10-100 A, which contradicts suggestions that MX tend to form microdomains of size 20-30 A in the glass. A marked change in the medium-range order (less than 10 A) is observed when MX is added to the binary M2O-nB2O3 glass. For AgI-doped glasses, a substantial increase in the medium-range order is manifested in a neutron diffraction peak at anomalously low Q values (Q = 0.8 A-1) increasing in strength with increasing AgI content. In contrast, for the LiCl-doped glasses, the ordering of the medium-range structure is observed to decrease. The Brillouin scattering experiments of the MX-doped borate glasses reveal a secondary relaxation process at gigahertz frequencies caused by fast ion diffusion. The Brillouin scattering data have been combined with data from lower-frequency experiments which results in a characterization of the dynamics of the mobile ions over ten decades of frequencies. The observations are compared with current models for fast ion diffusion in glasses. (author)