Determination of the sodium ion transference number of the Dion-Jacobson-type layered perovskite NaCa2Nb3O10 using ac impedance and dc methods

The electronic conductivity of the Dion - Jacobson-type layered perovskite NaCa2Nb3O10 was determined by employing ac impedance measurements using ion-blocking electrodes, electron-blocking electrodes, and dc Hebb-Wagner polarization measurements using NaCoO2 as the reversible reference electrode. Oxygen partial-pressure-dependent electrical conductivity studies revealed that the conductivity is nearly independent of the oxygen partial pressure in the range from 0.21 to 10(-6) atm. Open-circuit voltage measurements of a galvanic cell employing air and 2 ppm of O-2 in argon as electrodes revealed that layered perovskites appear not to be oxide ion conductors. The transference number for Na+ ions in NaCa2Nb3O10 at 550 degreesC is found to be 0.95 at the sodium activity of NaCoO2. The ac measurements using Na-beta-alumina with electron-blocking electrodes and Pt-nonblocking electrodes produced similar impedance data at 550 degreesC suggesting a high ionic nature, which is consistent with the polarization study. However, the ionic and electronic conductivities varied depending on the experimental conditions, such as temperature and partial pressures.