Microstructure, dielectric and ferroelectric properties of (NaxBi0.5)0.94Ba0.06TiO3 lead-free ferroelectric ceramics: Effect of Na nonstoichiometry

(NaxBi0.5)0.94Ba0.06TiO3 lead-free ferroelectric ceramics with x = 0.54, 0.50, 0.46, and 0.45 were prepared by solid state reaction of high energy ball milled powders. All ceramics exhibited typical diffraction peaks of ABO3 perovskite phase. A secondary phase peak was observed in the ceramic with x = 0.45. Relative amount of tetragonal phase was related to the amount of Na. The Na nonstoichiometry produced an ignorable effect on the mean grain size of the ceramics. The deficiency of Na in the ceramics weakened their dielectric anomalies corresponding to the transition from ferroelectric phase to the so-called “intermediate phase”. For the ceramics with Na nonstoichiometry, the degree of diffuseness of the transition from the “intermediate phase” to paraelectric phase increased. With changing Na amount from excess to deficiency, the “depolarization temperature” increased. The difference in dielectric and ferroelectric properties among the ceramics with various Na amount was associated with the generation of Na and/or oxygen vacancies.