Structural, thermal and electrical properties of Na_1+xAl_xTi_2-xP₃O₁₂ (x = 0.3) solid electrolytes

Investigation of the commercially available Na_1.3Al_0.3Ti_1.7(PO₄)₃ (NATP) solid electrolyte for Na-ion solid-state batteries (SIBs) application requires a comprehensive understanding of its microstructural, thermal behaviour and electrical properties. This study employed different physical, thermal, spectroscopic and microscopic techniques, including Archimedes’, XRD, SEM, DSC/TGA, dilatometry and impedance spectroscopy, to investigate the solid electrolyte properties of NATP. The X-ray diffraction and refinement results confirmed a rhombohedral structure with an R-3c space group for NATP and an F1 AlPO₄ space group impurity phase. A dilatometer and DSC/TGA studied the dimensional change, weight loss and heat flow of the NATP ceramic as a function of temperature. SEM measurement revealed loosely bonded particles of the ceramic microstructure with approximately 91.0% relative density by the geometric method. The optimum sintering temperature to suppressed/minimised AlPO₄ impurity phase was identified and phase refinement using Topas 5 software provided insight into the crystalline structure. NATP sample sintered at 900 °C for 12 h resulted in an ionic conductivity of 2.45 × 10⁻⁷ S/cm at 25 °C with an activation energy of 0.30 eV.