Effect of bismuth deficiency on structure and electrical properties of (Na0.5Bi0.5)0.93Ba0.07TiO3 ceramics

(Na_0.5Bi_x)_0.93Ba_0.07TiO₃ (x=0.500-0.492) ceramics were prepared by a citrate method, and the structure and electrical properties of the ceramics were investigated with respect to the amount of Bi deficiency. It was detected that the Bi deficiency had a considerable impact on the crystal structure and microstructure. The inspection of both the temperature dependence of the dielectric properties (free permittivity ε₃₃^T/ε₀ and dielectric loss tan δ) and the evolution of the polarization-electrical field (P-E) hysteresis loops with measuring temperature suggests that the Bi deficiency served to increase the depolarization temperature (T_d). The Bi deficiency led to an increase in the coercive field (E_c) and mechanical quality factor (Q_m) together with a decrease in the remanent polarization (P_r) and piezoelectric constants (d₃₃). The variation of the structure and electrical properties with Bi deficiency amount was qualitatively interpreted in terms of the formation of Bi and oxygen vacancies in the Bi-deficient specimens. This research indicates the importance of adequately controlling Bi stoichiometry of (Na_0.5Bi_0.5)_0.93Ba_0.07TiO₃ ceramics in obtaining the desired ferroelectric and piezoelectric properties.