Enhanced ionic conductivity in Mg-doped NASICON under high temperature and high pressure

Mg-doped Na Super Ionic Conductor (NASICON), a promising solid electrolyte material, has attracted extensive attention from the scientific research community due to its relatively high ionic conductivity and good electrochemical stability. However, its conductivity is still lower than that of liquid electrolytes. In this study, the high temperature and high pressure in situ AC impedance spectroscopy was employed to systematically investigate the electrical properties of Mg-doped NASICON, with the chemical formula Na3.2Zr1.9Mg0.1Si2PO12 (Mg–NZSP), under high temperature and pressure. The samples were synthesized by the solid-state reaction method. The experimental results show that at a constant temperature, the grain, grain boundary (GB), and total ionic conductivity of Mg–NZSP increase first, then decrease, and finally tend to be stable with the increase in pressure. Notably, the maximum conductivity is reached at 2.0 GPa. At a constant pressure, the ionic conductivity of Mg–NZSP is positively correlated with temperature. Regarding the study of dielectric properties, it is found that the relaxation time of sodium ions at the grain and GB in the Mg–NZSP prolongs with the increase in temperature, and its variation law follows the Arrhenius relationship. A giant dielectric constant phenomenon related to the space charge polarization of sodium ions was observed in the low frequency region.