Influence of Nb⁵⁺, Ti⁴⁺, Y³⁺ and Zn²⁺ doped Na₃Zr₂Si₂PO₁₂ solid electrolyte on its conductivity

In this study, Na₃Zr_2-xNb_0.8xSi₂PO₁₂, Na₃Zr_2-xTi_xSi₂PO₁₂, Na₃Zr_2-xY_xSi₂PO_12-0.5x, Na₃Zr_2-xZn_xSi₂PO_12-x ceramics with x = 0.1, 0.2, 0.3 and 0.4 were sintered to explore the influence of the valence state and the content of dopants on the conductivity of NASICON solid electrolyte. Archimedes method, X-ray diffraction, scanning electron microcopy and complex impedance spectroscopy were used to characterize the sintered samples. Results show that the dopant with +2 oxidation state cations improves the bulk conductivity mainly due to the less electrostatic interactions between Zn²⁺ ions and Na⁺ ions. The optimal doping content of Nb⁵⁺, Ti⁴⁺ and Y³⁺ doped NASICON ceramics is 0.1 mol and that of Zn²⁺ doped NASICON ceramic is 0.2 mol for the highest ionic conductivity. Among all the doped NASICON ceramics, Na₃Zr_1.8Zn_0.2Si₂PO_11.8 ceramic displays the highest total conductivity of 1.44 × 10⁻³ S/cm and bulk conductivity of 3.41 × 10⁻³ S/cm at room temperature. Furthermore, doping strategy both increases the density and decreases the sintering temperature of Na₃Zr₂Si₂PO₁₂ ceramic.