Transport of potassium ions in niobium phosphate glasses

The influence of Nb2O5 on the structure and ionic conductivity of potassium phosphate glasses was investigated in glasses with composition xNb(2)O(5)-(100-x)[0.45K(2)O-0.55P(2)O(5)], x = 10-47 mol%. The Raman spectra of glasses reveal a transition from predominantly orthophosphate to predominantly niobate glass network with increasing Nb2O5 content. In the glass structure, niobium forms NbO6 octahedra which are interlinked with phosphate units for the glass containing 10 mol% Nb2O5, but for higher Nb2O5 content they become mutually interconnected via Nb-O-Nb bonds. The transport of potassium ions was found to be strongly dependent on the structural characteristics of the glass network. While the mixed niobate-phosphate glass network hinders the diffusion of potassium ions by providing traps that immobilize them and/or by blocking the conduction pathways, predominantly niobate glass network exhibits a rather facilitating effect which is evidenced in the trend of DC conductivity as well as in the features of the frequency-dependent conductivity and typical hopping lengths of potassium ions.