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

Abstract

Sodium conductors were synthesized by means of doping metal oxide to Na 3Zr 2Si 2PO 12 (NASICON) which has been known as a sodium ion conductor with three-dimensional conduction path. A metal oxide (MgO, ZnO, Y 2O 3, TiO 2, SnO 2, V 2O 5, Nb 2O 5, Ta 2O 5) was added to the mixture of Na 2CO 3, ZrO 2, SiO 2 and NH 4H 2PO 4 in order to prepare the dense ceramics with high ionic conductivity. Tablets were sintered at temperatures between1100 and 1250°C. Doping of MgO or Nb 2O 5 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 ( ω cm) -1 at 300°C. The samples substitutedwith 2 mole% Mg 2+, V 5+, Nb 5+ or Ta 5+ for Zr 4+ 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 Nb 2O 5, the electronic conduction was found to be negligible by the measurement of the DC polarization method.