Sodium ionic conductivities of substituted NZP materials

Sodium zirconium phosphate [NZP] materials have been systematically classified and their sodium ionic conductivities and thermal activation energies given at 90 and 300°C. NaZr₂P₃O₁₂ has a low sodium ionic conductivity, which by some substitutions can be raised up to 6 orders of magnitude above the unsubstituted compound. The corresponding thermal activation energies range from 0.2 to 0.8 eV. Na_1+xZr₂Si_xP_3-xO₁₂ with 2 ≤ x ≤ 2.4 already has a high sodium conductivity which substitutions cannot significantly increase. The corresponding thermal activation energies show a tendency to decrease with higher temperature. The highest ionic conductivity in any NZP material is found for x = 2.2 in this system. Substitutions only decrease the sodium ionic conductivity.