Structural origin of electrical conductivity of copper lithium metaphosphate glasses

Abstract

We have sought the structural origin of the recently reported electrical conductivity of lithium copper phosphate glass system (50-x) Li2O-xCu2O-50 P2O5, as lithium oxide is gradually replaced by Cu2O. The structure of these glasses was determined by X-ray photoelectron spectroscopy, Fourier Transform Infrared Spectroscopy and Raman spectroscopy. The results show the presence of both mobile Cu+ and relatively immobile Cu2+ ions. The relative fraction of Cu2+ [Cu2+/Cutot] and non-bridging oxygen increases with x; the latter indicating a tendency towards depolymerization of the network. On the other hand, there is enhanced crosslinking within the network as PO⋯Li bonds are replaced by relatively covalent PO⋯Cu bonds. This leads to a more cross-linked structure and a progressive reduction of the optimum sites for the jumping of both Li+ and Cu+, in agreement with the observed increase of the energy barrier for ion transport as Li2O is replaced by Cu2O.