Insights into Ion-Network Interactions and Ion Transport in Glass

Abstract

Zusammenfassung We discuss the origins of mixed-former effects in borophosphate glasses of general composition: Li 0.5 BO 1.75 :(1−x)LiPO 3 and 0.4 Na 2 O:0.6 [xB 2 O 3 :(1−x)P 2 O 5 ], and show how these effects relate to changing ion-network interactions. In particular for the latter system, we analyse the permittivity spectra using the MIGRATION concept. The results show that the increase in the calculated “cage length” (spatial extent of localised ion motion) in the mixed former region correlates well with the increased abundance of the BO 4 tetrahedra. We propose that more local cation sites are created and fast electronic bond-switching processes open up these sites to facilitate macroscopic transport. This picture of ion transport independent of network dynamics accounts for all favourable effects observed in mixed former glasses such as increase in ion mobility, rise in T g and improvement in chemical durability.