Effect of excess of bismuth doping on dielectric and ferroelectric properties of BaBi4Ti4O15 ceramics

Abstract The effect of excess bismuth oxide Bi2O3 (2–10 wt%) for processing BaBi4Ti4O15 (BBT) ceramics by solid state reaction has been investigated. The formation of a single phase and a change in the orthorhombic distortion are confirmed with varying excess of bismuth content. Changes in the density are marginal, and use of excess bismuth is seen to promote enhanced grain growth. Dielectric response is improved markedly exhibiting reduced dielectric losses and dispersion over a wide frequency range (10−3–106 Hz). A high dielectric constant (e′~226), low loss factor (tan δ~0.01) and low dc conductivity (σdc~10–14 Ω−1 cm−1) are achieved with an optimum content 6–8 wt% of excess of bismuth oxide. Temperature dependent dielectric data fits well to the modified Curie–Weiss law and the frequency dependent maximum temperatures (Tm and Tm1) corresponding to real and imaginary parts of dielectric permittivity (e′ and e″) show a good fit to the non-linear Vogel–Fulcher (V–F) relationship. A clear relaxor behavior is observed with a degree of diffuseness, γ~1.97. Saturated hysteresis loops with high remnant polarization (Pr~12.5 μC/cm2), low coercive fields (Ec~26 kV/cm) are measured and a high piezoelectric coefficient (d33~29 pC/N) is achieved in poled BaBi4Ti4O15 ceramics prepared with up to 8 wt% of excess bismuth oxide. Such a relaxor ferroelectric material with high Curie temperature is useful for high temperature piezoelectric transducer applications.