STRUCTURE OF FAST-ION CONDUCTING BORATE GLASSES BY NEUTRON-DIFFRACTION AND REVERSE MONTE-CARLO SIMULATIONS

The structures of the two fast ion conducting glass systems (AgI)(x) (Ag2O-2B(2)O(3))(1-x) and (LiCl)(x) (Li2O-2B(2)O(3))(1-x) have been examined. The neutron diffraction experiments revealed large similarities in the short range order of the B-O network for the two glass systems. However, remarkable differences are observed for the intermediate range order. This is evident from the low-Q part of the total structure factor; the first sharp diffraction peak (FSDP) at 1.6 Angstrom(-1) is almost unaffected by LiCl doping, while in the case of AgI doping a new strong low-and peak appears at about 0.8 Angstrom(-1). To investigate the underlying structural differences Reverse Monte Carlo (RMC) simulations have been performed. The simulations show that the experimental FSDPs are caused mainly by density fluctuations in the B-O network. The anomalous low-Q peak of the AgI doped glasses is thus explained by that AgI locally expands the B-O network and causes longer range correlations between borate groups. The network have larger density fluctuations and voids, which, in turn, are beneficial for the formation of open pathways in which the cations can move.