Solid-state ionics - conductivities of Na+ ion conductors based on NASICON

Sodium conductors were synthesized by means of doping metal oxide to Na3Zr2Si2PO12 (NASICON) which has been known as a sodium ion conductor with three-dimensional conduction path. A metal oxide (MgO, ZnO, Y2O3, TiO2, SnO2, V2O5, Nb2O5, Ta2O5) was added to the mixture of Na2CO3, ZrO2, SiO2 and NH4H2PO4 in order to prepare the dense ceramics with high ionic conductivity. Tablets were sintered at temperatures between1100 and 1250°C. Doping of MgO or Nb2O5 resulted in the formation of dense samples with the apparent density higher than that of undoped polycrystalline NASICON. Electrical conductivities were measured using an AC impedance bridge at 10 kHz. The conductivity of NASICON prepared as starting material was 6.4 × 10-2 (ωcm)-1 at 300°C. The samples substitutedwith 2 mole% Mg2+, V5+, Nb5+ or Ta5+ for Zr4+ showed conductivities of 1.6 × 10-1, 1.4 × 10-1, 1.3 × 10-1, 1.1 × 10-1 (ω cm)-1 at 300°C, respectively, all of which were higher than that of NASICON. In the case of the samples doped with MgO or Nb2O5, the electronic conduction was found to be negligible by the measurement of the DC polarization method.