Structural disorder and enhanced ion transport in amorphous conductors

Conductivity (σ) data are reported for Li₂B₄O₇ and LiBO₂ crystals. While the σ behavior of boracite glass has been suggested to be comparable to its fast ion conducting (FIC) crystalline form, diborate and metaborate glasses are observed to be substantially better conductors than their crystalline counterparts. Both here and in the literature, framework disorder can be associated with enhanced σ's. Data on density and lithium vibration spectra are considered in a critical analysis of the borate structures. The distribution of anionic species about the framework, and in turn, about interstices in the carrier sublattice, is shown to influence critically the transport behavior. Paradigms for FIC are reevaluated in light of a closer inspection of structure-transport relationships in polymorphic materials.