Effects of site engineering and doped element types on piezoelectric and dielectric properties of bismuth ferrite lead-free ceramics

Abstract

Poor piezoelectric activity is often observed in BiFeO₃ ceramics due to their low resistivity and high coercive field, which can easily result in piezoelectric breakdown before the domains are switched. Here, we attained a high piezoelectricity using a series of bismuth ferrite ceramics substituted by rare earth elements and transition metal elements {e.g., Bi_0.925La_0.05A_0.025FeO₃, A: Sm, Yb, Ho, Y, Nd, Pr, Dy, Gd; Bi_0.925La_0.05Sm_0.025Fe_0.95M_0.05O₃, M: Sc, In, Al, Ga, Ni, Co} fabricated using the conventional solid-state method. The influences of site engineering (e.g., Bi site or Fe site) as well as the doped element types on their phase structure, microstructure, and electrical properties have been comparatively analyzed. The ions (e.g., A = Sm, Yb, Ho, and Y) substituting at the Bi site are helpful to attain both a pure phase structure and a relatively good piezoelectricity (d₃₃ ≥ 40 pC N⁻¹) for BFO ceramics, while ion substitutions at the Fe site cannot suppress the formation of impurity phases which results in degraded electrical properties. Both XRD and backscattered electron images fully confirmed the existence of impurity phases (Bi-rich and Fe-rich counterparts) in the ceramics doped by Ga. According to the related experiments, the piezoelectric properties of bismuth ferrite ceramics can be promoted by site engineering as well as the optimization of the element types. This result will point out a way for us to promote the piezoelectric properties of bismuth ferrite ceramics through choosing both suitable doping elements and eliminating impurity phases.