Na-V-P-Nb-based materials have gained substantial recognition as cathode materials in high-rate sodium-ion batteries due to their unique properties and compositions, comprising both alkali and transition metal ions, which allow them to exhibit a mixed ionic–polaronic conduction mechanism. In this study, the impact of introducing two transition metal oxides, V₂O₅ and Nb₂O₅, on the thermal, (micro)structural, and electrical properties of the 35Na₂O-25V₂O₅-(40 − x)P₂O₅ − xNb₂O₅ system is examined. The starting glass shows the highest values of DC conductivity, σ_DC, reaching 1.45 × 10⁻⁸ Ω⁻¹ cm⁻¹ at 303 K, along with a glass transition temperature, T_g, of 371 °C. The incorporation of Nb₂O₅ influences both σ_DC and T_g, resulting in non-linear trends, with the lowest values observed for the glass with x = 20 mol%. Electron paramagnetic resonance measurements and vibrational spectroscopy results suggest that the observed non-monotonic trend in σ_DC arises from a diminishing contribution of polaronic conductivity due to the decrease in the relative number of V⁴⁺ ions and the introduction of Nb₂O₅, which disrupts the predominantly mixed vanadate–phosphate network within the starting glasses, consequently impeding polaronic transport. The mechanism of electrical transport is investigated using the model-free Summerfield scaling procedure, revealing the presence of mixed ionic–polaronic conductivity in glasses where x < 10 mol%, whereas for x ≥ 10 mol%, the ionic conductivity mechanism becomes prominent. To assess the impact of the V₂O₅ content on the electrical transport mechanism, a comparative analysis of two analogue series with varying V₂O₅ content (10 and 25 mol%) is conducted to evaluate the extent of its polaronic contribution.

In this study, the nature of the electrical transport and structural changes resulting from the systematic substitution of Al₂O₃ with K₂O in 40P₂O₅-(25−x)Al₂O₃-35Na₂O-xK₂O, where x = 5.0, 7.5, 10.0, 12.5, and 15.0 mol% (PANxK), is investigated. The impact of the changes in glass structure and its correlation to electrical properties is presented. The mixed alkali effect (MAE) is observed due to the presence of two different alkali oxides, resulting in a non-monotonic trend in the studied glass properties. The infrared spectra show the shift and diminishing of the bands related to the P–O–P/P–O–Al bridges with increasing K₂O content and changes in bands related to depolymerization of the glass network, which is confirmed by the trend of the Tg values. The minimum value of DC conductivity is obtained for glass with x = 12.5 mol%. With the overall increase in alkali content, the number of non-bridging oxygens increases, also affecting the conductivity values. Frequency-dependent conductivity spectra analyzed by Summerfield, Baranovskii-Cordes and Sidebottom scaling procedures revealed interesting features and signature of the MAE in the short-range dynamics of the potassium and sodium ions, both for individual glass composition and glass series as a whole. This study showed the impact of MAE and local glass structure on the electrical features and the prevailing of one effect over the other as a function of the glass composition. MAE dominates in a wider range, but with the significant increase in alkali content, MAE is consequently overpowered.

Sodium-phosphate-based glass-ceramics (GCs) are promising materials for a wide range of applications, including solid-state sodium-ion batteries, microelectronic packaging substrates, and humidity sensors. This study investigated the impact of 24 h heat-treatments (HT) at varying temperatures on Na-Ge-P glass, with a focus on (micro)structural, electrical, and dielectric properties of prepared GCs. Various techniques such as powder X-ray diffraction (PXRD), infrared spectroscopy-attenuated total reflection (IR-ATR), and scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS) were employed. With the elevation of HT temperature, crystallinity progressively rose; at 450 °C, the microstructure retained amorphous traits featuring nanometric grains, whereas at 550 °C, HT resulted in fully crystallized structures characterized by square-shaped micron-scale grains of NaPO₃. The insight into the evaluation of electrical and dielectric properties was provided by Solid-State Impedance Spectroscopy (SS-IS), revealing a strong correlation with the conditions of controlled crystallization and observed (micro)structure. Compared to the initial glass, which showed DC conductivity (σ_DC) on the order of magnitude 10⁻⁷ Ω⁻¹ cm⁻¹ at 393 K, the obtained GCs exhibited a lower σ_DC ranging from 10⁻⁸ to 10⁻¹⁰ Ω⁻¹ cm⁻¹. With the rise in HT temperature, σ_DC further decreased due to the crystallization of the NaPO₃ phase, depleting the glass matrix of mobile Na⁺ ions. The prepared GCs showed improved dielectric parameters in comparison to the initial glass, with a noticeable increase in dielectric constant values (~20) followed by a decline in dielectric loss (~10⁻³) values as the HT temperatures rise. Particularly, the GC obtained at @450 stood out as the optimal sample, showcasing an elevated dielectric constant and low dielectric loss value, along with moderate ionic conductivity. This research uncovers the intricate relationship between heat-treatment conditions and material properties, emphasizing that controlled crystallization allows for precise modifications to microstructure and phase composition within the remaining glassy phase, ultimately facilitating the fine-tuning of material properties.

Sodium-phosphate-based glass-ceramics (GCs) are promising materials for a wide range of applications, including solid-state sodium-ion batteries, microelectronic packaging substrates, and humidity sensors. This study investigates the impact of 24-hour heat-treatments at varying temperatures on Na-Ge-P glass, with a focus on (micro)structural, electrical, and dielectric properties of prepared GCs. Various techniques such as powder X-ray diffraction (PXRD), infrared spectroscopy-attenuated total reflection (IR-ATR), and scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS) are employed. With the elevation of heat-treatment temperature, crystallinity progressively rises; at 450 °C, the microstructure retains amorphous traits featuring nanometric grains, whereas at 550 °C, heat-treatment results in fully crystallized structures characterized by square-shaped micron-scale grains of NaPO3. The insight into the evaluation of electrical and dielectric properties is provided by Solid-State Impedance Spectroscopy (SS-IS), revealing a strong correlation with the conditions of controlled crystallization and observed (micro)structure. The glass-ceramic heat-treated at 450 °C achieves the highest DC conductivity of 2.30×10–8 Ω–1 cm–1 at 393 K. As the heat-treatment temperature rises, the crystallization of the NaPO3 phase depletes the glass matrix of mobile Na+ ions, resulting in a reduction in DC conductivity. Dielectric parameters also decrease with rising heat-treatment temperature, with the glass-ceramic heat-treated at 550 °C displaying the lowest permittivity of 19.37 and the dielectric loss of 0.008. This research uncovers the intricate relationship between heat-treatment conditions and material properties, emphasizing that controlled crystallization allows for precise modifications to microstructure and phase composition within remaining glassy phase, ultimately facilitating fine-tuning of material properties.