Enhancement of sodium ion conductivity in phosphate-based glass-ceramics by chemical substitution approach

A NASICON-type sodium-ion conducting material was synthesized via the glass-ceramic route by investigating the zinc doped Na₂O–Al₂O₃–TiO₂–P₂O₅ system. The glasses and glass-ceramics corresponding to the formula Na_2+xAl_1-xZn_xTi(PO₄)₃ (x = 0, 0.2, 0.4, 0.6, 0.8, 1), labeled as (NAZTP-G_x) and (NAZTP-GC_x) respectively, were characterized using different techniques. Differential Scanning Calorimetry (DSC) measurements were carried out to identify the characteristic temperatures, the glass transition (T_g) and the crystallization temperature (T_c). X-ray Diffraction (XRD) analysis of the glass-ceramics confirmed the formation of a solid solution Na_2+xAl_1-xZn_xTi(PO₄)₃ NASICON phase, Theoretical calculations employing the Perdew–Burke–Ernzerhoff generalized gradients approximation (PBE-GGA) model supported the potential substitution of aluminum by zinc in the octahedral site in the NASICON-phase. Further structural insights were obtained through Infrared (IR) and Raman spectroscopies. Scanning electron microscopy (SEM) analysis revealed a distinct flower-like shape of the formed crystallites in the glass-ceramic NAZTP-GC_0.2. Electrical characterization using electrochemical impedance spectroscopy (EIS) demonstrated that the NAZTP-GC_0.2 sample exhibited the highest ionic conductivity at 300 °C, reaching 4.1 × 10⁻⁵ (Ω⁻¹ cm⁻¹) with an activation energy of 0.25 eV. The DC polarization was performed on the NAZTP-GC_0.2 glass-ceramic, revealing that the ions are the main charge carriers in the sample. This comprehensive analysis provides valuable insights into the partial zinc doping of NASICON glass-ceramics, offering potential for improved performance as solid electrolytes in various applications.