Study of the structure, dielectric and ferroelectric behavior of BaBi_4+δTi₄O₁₅ ceramics

The structure and ferroelectric properties of excess bismuth doped barium bismuth titanate BaBi_4+δTi₄O₁₅ (δ = 2 - 10 wt.%)) ceramics prepared by solid-state reaction method have been investigated. X-ray diffraction (XRD) confirms the formation of a single phase material with a change in the orthorhombic distortion with varying excess of bismuth content. There is no change in the phase transition temperature (T_m) while the relaxor behaviour has been modified significantly with excess of bismuth doping. Saturated hysteresis loops with high remnant polarization (P_r ~ 12.5 µC/cm²), low coercive fields (E_c ~ 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. The improvement in the ferroelectric properties with increase in the excess bismuth content in BaBi₄Ti₄O₁₅ ceramics has been explained in terms of changing oxygen vacancy concentration and structural relaxation. Tunable ferroelectric materials can be obtained by manipulating the doping amount of excess bismuth.