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Structural and electrical studies of sodium vanadium niobium phosphate glasses and glass-ceramics

Sodium phosphate-based glasses have been proposed as safer, cheaper, and environmentally friendly materials for electrolytes and/or electrode materials in solid-state battery development. Despite their advantages, given glasses usually suffer from relatively low ionic conductivity. Hence, to improve the electrical conductivity of these materials, new research seeks to clarify the relationship between composition, structure, and electrical properties. Numerous studies showed that significant improvement in electrical conductivity can be achieved when one glass- forming oxide is replaced by another that causes non-linear variation of conductivity, a phenomenon known as the mixed glass former effect (MGFE). In addition, crystallization of given glasses, brought about either by controlled heat-treatment or by spontaneous crystallization at the border of the glass-forming composition region, has been recognized as another approach to improve overall electrical conductivity, since it leads to glass- ceramic materials with substantially improved electrical features.[1, 2] In the present work, two series of glasses are prepared by conventional melt-quenching technique from the quaternary system Na2O–V2O5–P2O5–Nb2O5. The content of V2O5 is kept constant, while P2O5 is gradually replaced by Nb2O5, in order to investigate the compositional dependence of glass- forming tendency and to verify the MGFE in the presence of two conditional glass-formers, V2O5 and Nb2O5. The PXRD technique is used to confirm the amorphous character of the prepared glasses, as well as to qualitatively and quantitatively study partially crystallized samples formed by spontaneous crystallization during cooling of high content Nb2O5 glass melts. The thermal behaviour of the obtained glass-(ceramics) is analyzed by DTA, while their (micro)structural properties are evaluated by SEM-EDS analysis and IR-ATR spectroscopy. On the other hand, their electrical properties are investigated by solid-state impedance spectroscopy (SS-IS) in a wide range of frequencies (0.01 Hz – 1 MHz) and at different temperatures (-90 °C – 240 °C). The relationship between the structural changes that occur upon exchange of glass-formers along with certain physico-chemical properties of obtained glass- (ceramics) is discussed in detail. 1. M. Storek, M. Adjei-Acheamfour, R. Christensen, S. W. Martin, R. Böhmer, J. Phys. Chem. B 120 (2016) 4482–4495. 2. T. K. Pietrzak, M. Wasiucionek, J. E. Garbarczyk, Nanomaterials 11 (2021) 1321–1345.

glass ; glass-ceramic ; structural properties ; electrical properties

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