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 xNb₂O₅–(100-x)0.45K₂O–0.55P₂O₅], 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.