SODIUM IONIC CONDUCTIVITIES OF SUBSTITUTED NZP MATERIALS

An important group of sodium ionic conductors is the sodium zirconium phosphate [NZP] materials which are framework crystal structures with corner linked Zr-O octahedra and P-O tetrahedra. The interstitial open network allows sodium ions to migrate. The basic NZP formula is NaZr2 P3O12, and the structure formula is [M1'] [M2''] [A2VI] [B3IV]O12, whe re M' and M'' are interstitial sites occupied partially or fully by Na or other substituting ions. A or B lattice sites are occupied by Zr a nd P, respectively, or by possible substituting ions. A large number o f authors have reported sodium ionic conductivities and thermal activa tion energies at different temperatures of NZP materials with a large number of substitutions. In this study the reported NZP materials have been systematically classified and their sodium ionic conductivities and thermal activation energies given at 90 and 300-degrees-C. NaZr2P3 O12, has a low sodium ionic conductivity, which by some substitutions can be raised up to 6 orders of magnitude above the unsubstituted comp ound. The corresponding thermal activation energies range from 0.2 to 0.8 eV. Na1+xZr2SixP3-xO12 with 2 less-than-or-equal-to x less-than-or -equal-to 2.4 already has a high sodium conductivity which substitutio ns cannot significantly increase. The corresponding thermal activation energies show a tendency to decrease with higher temperature. The hig hest ionic conductivity in any NZP material is found for x = 2.2 in th is system. Substitutions only decrease the sodium ionic conductivity.