engleski

Transport properties of potassium cations in Nb2O5- P2O5-based glasses

Niobium phosphate glasses belong to an important class of oxide glasses and have functional properties thus making them attractive for various applications, such as waste form for radioactive immobilization, glass fibers, and optical lenses. Moreover, niobium oxide can be incorporated in combination with alkali oxides in a phosphate network in a wide composition range, which makes these glasses interesting for electrical applications and electrode/electrolyte materials for solid-state batteries. In this study, the structural and electrical properties of glasses with composition xNb2O5-(100-x)[0.45K2O-0.55P2O5], x=10-50 mol% are investigated by Raman (RS) and Impedance spectroscopy (IS). The glasses are synthesized by microwave heating. The melts are quenched in air by pouring into steel moulds and annealing at 773 K for 3 hours. Raman spectra show 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, the niobium forms NbO6 octahedra interlined with phosphate units (x=10 mol%), and is mutually interconnected via Nb-O-Nb bonds at higher Nb2O5 content. The DC conductivity decreases with increasing Nb2O5 content as the concentration of potassium ions (K+) decrease. Interestingly, this decrease is not linear suggesting that the glass structure strongly influences the transport of potassium ions. While glasses with predominant orthophosphate structure and those with predominant niobate glass network show a slight decrease in DC conductivity with increasing Nb2O5 content, the intermediate glass compositions exhibit a sharp drop in DC conductivity, which could be attributed to the hampering effect of the mixed niobate-phosphate network on the diffusion of potassium ions. Remarkably, a predominantly niobate glass network exhibits a rather facilitating effect which is evident not only in the trend of DC conductivity but also in the features of the frequency-dependent conductivity and the typical hopping lengths of the potassium ions. All glasses obey both Summerfield and Sidebottom scaling procedures of conductivity spectra indicating that the conductivity mechanism does not change with the temperature.

glass structure ; ionic conductivity ; niobium phosphate glasses

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