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Structural and electrical study of sodium phosphate glass-(ceramics) containing niobium(V) and vanadium(V) oxides

Sodium phosphate-based glasses offer a promising alternative to the commonly used, high-cost lithium materials for the development of solid- state batteries for use as electrolytes and electrode materials. Although these glasses show lower electrical conductivity than the lithium ones, recent research demonstrates that a significant increase in ionic conductivity can be achieved by the addition of another glass-forming oxide (the so-called mixed glass-former effect, MGFE) [1]. Of particular interest is the study of glass systems in which the conventional glass- forming oxide (P2O5) is replaced by transition metal oxides (TMO) such as Fe2O3, MoO3, WO3, V2O5 and Nb2O5, known as conditional glass formers. In addition to the enhancement of ionic conductivity due to induced structural changes, TMOs also contribute to the overall electrical conductivity by electron hopping between TM ions in different oxidation states [2]. In this study, glasses of the quaternary system Na2O–V2O5–P2O5–Nb2O5 are prepared by the conventional melt-quenching method. In order to investigate the MGFE and glass-forming tendency, the content of Na2O and V2O5 is constant, while P2O5 is gradually replaced by Nb2O5. The amorphous character of prepared glasses is confirmed by PXRD technique, whereas the partially crystallized samples, obtained by spontaneous crystallization which occurs at high Nb2O5 content, are qualitatively and quantitatively analysed. The (micro)structure of the obtained glass-(ceramics) is investigated by SEM-EDS analysis and IR-ATR spectroscopy, while their thermal properties are determined by DTA. The electrical properties of studied samples are investigated in detail by solid-state impedance spectroscopy (SS-IS) in a wide frequency (0.01 Hz– 1 MHz) and temperature range (-90 °C–240 °C). The results of this research shed light on the relationship between the composition, (micro)structure and electrical properties of the selected system, which is of the utmost importance for the development of materials with the possibility of fine-tuning the desired electrical properties. [1] Storek, M., Adjei-Acheamfour, M., Christensen, R., Martin, S. W., Böhmer, R., J. Phys. Chem. B 120 (2016) 4482–4495. [2] S. Renka, L. Pavić, G. Tricot, P. Mošner, L. Koudelka, A. Moguš-Milanković, A. Šantić, Phys. Chem. Chem. Phys. 23 (2021) 9761–9772.

Phosphate glasses, Structural properties, Electrical properties, Impedance spectroscopy

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