Tailoring Structure for Improved Sodium Mobility and Electrical Properties in V2O5–Nb2O5–P2O5 Glass(es)-(Ceramics)

This study investigates the influence of structural modifications induced by the introduction of Nb2O5 on the thermal, (micro)structural, and electrical properties of quaternary system 35Na2O–10V2O5-(55–x)P2O5-xNb2O5 (x = 0–40 mol%). Non-monotonic trends in DC conductivity and activation energy are attributed to the facilitating effect of Nb2O5 on the transport of Na + ions, confirming the mixed glass former effect. The results demonstrate that the electrical conductivity mechanism is purely ionic, with V2O5 acting as both, glass modifier and network-former with vanadate units being in predominantly 4-fold coordination and without actively participating in the conduction process. Complementary Raman and IR-ATR spectroscopic studies in combination with solid-state impedance spectroscopy (SS-IS) reveal a strong correlation between structural and electrical properties indicating that the enhancement in conductivity is driven by the formation of mixed niobate-phosphate glass network. The increase in conductivity is followed by a gradual transition of glass structure from a predominantly phosphate glass network (x ≤ 10, Region I) into a mixed niobate-phosphate glass network (10 ≤ x ≤ 20, Region II). The conductivity increases by a factor of ∼4.5 within the series reaching the highest value of 3.29 × 10−10 Ω−1 cm−1 for Nb-20 glass. In the predominantly niobate network (x ≥ 25, Region III), the 3D clustering of NbO6 octahedra hinders the transport of Na + ions. The scaling features of the conductivity spectra additionally confirm the ionic mechanism of electrical transport and provide insight into the local dynamics of Na+ ions.