Preparation and characteristic of NASICON ceramics

Hot-pressed sintering was employed to prepare the sodium super ionic conductor (Na_1+x Zr₂Si_xP_3-xO₁₂, 1.8≤x≤2.2) ceramics and compare with the sample obtained from normal-press sintering. The phase formation, density, and conductivity of the hot-press sintered and the normal-press sintered samples were investigated in detail. Results show that the density of NASICON ceramics and the degree of crystallization can be improved by hot-press process efficiently. The density of the sample sintered by normal sintering is obviously lower than that sintered by hot press. XRD analysis indicates all the hot press sintered samples contain mainly monoclinic NASICON and no ZrO₂ phase was found. The ionic conductivity of normal-press sintered sample is much lower than that of hot-press sintered sample. When the composition is close to Na₃Zr₂Si₂PO₁₂, the dc conductivities of the hot press sintered samples were in the order of 10^-3 S·cm^-1. The variation of the ac conductivity with frequency in the high frequency region agrees with the power law feature of σ(ω) ∝ ωⁿ (0<n<1).