| Popis: |
Niobium phosphate glasses belong to an important class of oxide glasses and have been investigated for a wide range of applications, such as the waste form for radioactive waste immobilization, glass fibers, and optical lenses, and electrode/electrolyte materials for solid-state batteries. In this study, structural and electrical properties of glasses with composition xNb2O5-(100-x)[0.45K2O-0.55P2O5], x=10-50 mol% were investigated by Raman and impedance spectroscopies. Glasses were synthesized by microwave heating of starting chemicals NH4H2PO4, Nb2O5, and KOH in a microwave oven with a nominal power of 1100 W for 30 min. The melts were quenched in the air by pouring them into steel molds and were annealed for 3 h at 773 K. Raman spectra reveal that the glass structure changes from predominantly orthophosphate (x≤20 mol%) to predominantly niobate (x=50 mol%) with increasing Nb2O5 content. In the glass network, niobium forms NbO6 octahedra which becomes mutually interconnected via Nb-O-Nb bonds at higher Nb2O5 content. The DC conductivity of glasses decreases with the increase in Nb2O5 due to a decrease in the concentration of potassium ions, however, this decrease is not linear indicating that glass structure strongly influences their mobility. While glasses with predominantly orthophosphate structure and those with predominantly niobate glass network exhibit a slight decrease in DC conductivity with increasing Nb2O5 content, the intermediate glass compositions exhibit a strong drop in DC conductivity which could be attributed to the hampering effect of the mixed niobate-phosphate network on the diffusion of potassium ions. Interestingly, a predominantly niobate glass network exhibits a rather facilitating effect which is evidenced not just in the trend of DC conductivity but also in the features of the frequency-dependent conductivity and typical hopping lengths of potassium ions. |
