The medium-range order in Li and Ag borate glasses (with AgI)

Abstract

Models are proposed for the medium-range order (MRO) in ion-conducting Ag and Li borate glasses, (Ag2O · 2B2O3)1 - x(AgI)x and (Li2O · 2B2O3). The analysis of the Ag diborate glass was made on the basis of both neutron and X-ray scattering data. The model comprises an arrangement of diborate cages at a distance of ⋍ 6 Å, the Ag atoms being attached to these cages by AgO bonds 1.8 and 2.1 Å. The large X-ray scattering peak located at 2.2 Å−1 then corresponds to the AgAg ordering distance of 3.1 Å. In the sequence Ag diborate, tetraborate, octaborate, the shift in the position of the large X-ray peak from 2.25 to 1.87 Å−1 is explained by an increase in the AgAg separation from 3.10 to 3.75 Å. For the Li diborate glass there is a complete disappearance of the MRO as characterized for example by cages and/or tetraborate units.