Investigation of structural, thermal, and electrical properties of sodium-doped oxynitride glass-ceramics

This study aimed to investigate the influence of Na₂O addition on the structural, thermal, and electrical characteristics of oxynitride glass-ceramics within the Na–K–Mg–Ca–Al–Si–O–N system. Oxynitride glass-ceramic samples were prepared via spark plasma sintering (SPS) with sodium oxide doping levels ranging from 0 wt% to 12 wt%. FESEM analysis revealed changes in sample morphology with increasing sodium content, indicating the formation of granular structures and sodium-rich clusters in the glass matrix. XRD revealed the presence of nanocrystalline phases in doped samples, primarily (Na,Ca)(Si,Al)₄O₈. IR spectroscopy demonstrated changes in the glass network structure due to sodium, affecting both silicate and aluminum units. Increasing sodium content led to higher crystallinity and a corresponding decrease in sample density. The thermal expansion increased notably with sodium content, attributed to the disruptive effect of sodium ions on the glass-ceramics structure, while thermal conductivity decreased also attributed to this disruption. AC conductivity increased significantly with sodium, indicating enhanced ionic conductivity, while DC conductivity was observed in doped samples at higher temperatures, with activation energies consistent with ionic conduction mechanisms. The exponent-dependent (s) parameter decreased with higher sodium content, suggesting limited ion diffusion.