Study on structural and electrical properties of layered perovskite-type oxide-ion conductor

Samples of BINAVOX (Bi2NaxV1−xO5.5−2x), in the composition range 0 ≤ x ≤ 0.20 were synthesized by sol–gel citrate route. Thermal decomposition and phase structure were characterized using FT-IR, Powder X-ray diffraction and simultaneous thermogravimetric and differential thermal analysis. It has been found that BINAVOX xerogels are completely calcinated above 550 °C for 3 h of thermal treatments. Furthermore, the highly conducting γ-phase was stabilized for compositions with x ≥ 0.15. AC impedance spectroscopy revealed that the diffusion of oxide-ion vacancies is thermally activated in both grain interiors and boundaries. In general, the relaxation time of grain boundaries contribution is two orders of magnitude higher than that of grain interiors. The dielectric permittivity showed a general decay with the increase in sodium substitution. Importantly, the composition dependence of electrical conductivity exhibited a maximum for x = 0.13 at lower temperatures (σ300 ∼ 1.34 × 10−5 S cm−1), which is attributed to the reduction in the activation energy of conduction.