Mechanical and dielectric relaxation studies on the fast oxide ion conductor Na0.54Bi0.46TiO2.96

• The bulk oxide ionic conductivity of the Na0.54Bi0.46TiO2.96 sample at 673 K is about 1.6 × 10− 3 S/cm, nearly five times higher than that of the Na0.5Bi0.5TiO3 sample.
• Judging from the relaxation parameters (around 0.76 eV, 10− 12 s), the relaxation peak is caused by the oxide ion diffusion by the Na–Bi–Ti pathways in the Na0.54Bi0.46TiO2.96 sample.
• Compared with the Na0.5Bi0.5TiO3 compound, the phase transition temperature of the ferroelectric to anti-ferroelectric phase in the Na0.54Bi0.46TiO2.96 sample increases from about 430 K to 495 K.

The electrical properties and the mechanism of oxide ion diffusion in the Na0.54Bi0.46TiO2.96 compounds were investigated. The bulk ionic conductivity of the Na0.54Bi0.46TiO2.96 sample at 673 K is about 1.6 × 10− 3 S/cm, nearly five times higher than that of the Na0.5Bi0.5TiO3 sample at the same temperature. In the internal friction measurement, a prominent relaxation peak was observed around 340 K at the measuring frequency 1 Hz. As for the dielectric measurement, the relaxation peak was observed above 450 K when the measurement frequency is greater than 500 Hz. The activation energy and the preexponential factor of the relaxation time measured were determined as (0.76 eV, 0.72 × 10− 12 s) and (0.77 eV, 1.8 × 10− 12 s) for the internal friction measurement and the dielectric measurement, respectively. The relaxation parameters are in the same range as that for oxide ion diffusion in the perovskite oxide ion conductors, indicating that the relaxation peak may be caused by the oxide ion diffusion by the Na–Bi–Ti pathways in the Na0.54Bi0.46TiO2.96 sample. In additional, compared with the Na0.5Bi0.5TiO3 sample, the phase transition temperature of the ferroelectric phase to the anti-ferroelectric phase in the Na0.54Bi0.46TiO2.96 sample increases from about 430 K to 495 K, widening the application temperature range of the Na0.5Bi0.5TiO3-based materials. These results demonstrated that the Na0.5Bi0.5TiO3-based material system is promising as fast oxygen ionic conductors and the application temperature range of the Na0.5Bi0.5TiO3-based materials can be widened with the bismuth ion partly substituted by the sodium ion, which is meaningful to improve the ferroelectric and piezoelectric performance of Na0.5Bi0.5TiO3-based materials.