Fast Li+ ion conductance in chloroborate glasses II-diborates and metaborates

The understanding of FIC in amorphous materials is limited in part due to a lack of reliable structural models. Alkali oxide additions to B₂O₃ are known to modify the glass network initially by the formation of BO₄-tetrahedral units at the expense of trigonal BO₃ units. Our recent studies on the system 36.4 mol%Li₂Z(Z=0,Cl₂)-63.6 mol% B₂O₃ demonstrate that major structural changes in the network also accompany the large increases in ion conductivity upon the replacement of oxygen with chlorine. In the present study, the scope of our investigation has been extended to glasses of composition Li₂Z.2B₂O₃ (diborate) and Li₂Z.B₂O₃ (metaborate). This enables us to study glasses at several different total Li contents lying in different regimes of network structure, as a function of Cl additions. Results of extensive measurements of electrical conductivity, glass transition and density as a function of glass composition and temperature are used to emphasize the importance of considering structural changes along with ion transport variations upon modification of glass composition. Suggestions for the cause of observed structure-transport relations are presented.