INTERMEDIATE-RANGE STRUCTURE OF FAST-ION-CONDUCTING AGI-DOPED MOLYBDATE AND TUNGSTATE GLASSES

The structures of two fast-ion-conducting molecular glasses, (AgI)(0.7 5)(Ag2MoO4)(0.25) and (AgI)(0.75)(Ag2WO4)(0.25), have been investigate d by neutron and x-ray diffraction. Both molybdate and tungstate glass es show a first sharp diffraction peak (FSDP) at very low Q-values (0. 65 Angstrom(-1) and 0.55 Angstrom(-1) respectively) in the neutron dat a. However, only weak peaks are observed at similar Q-values in the x- ray data. The diffraction results have been used to model the structur es using the reverse Monte Carlo (RMC) method. The RMC results show th at all partial structure factors contribute to the FSDP except S-AgAg, S-AgI, S-II and S-MoMo (or S-WW). This implies that the origin of the FSDP is somewhat different from that for the berate and phosphate gla sses where S-BB and S-PP (the corresponding centres of the covalently bonded oxide groups) contribute strongly to the prepeak. The result ex cludes any simple explanation of the FSDP in terms of AgI clustering.