Tailoring electrical properties of BiFeO3–BaTiO3 ceramics via A-site La3+ substitution: suppressed leakage and enhanced strain

Abstract

To tailor the electrical properties of 0.7BiFeO₃–0.3BaTiO₃ (BFO–BTO) lead-free ceramics, a series of A-site La³⁺-doped 0.7Bi_1−xLa_xFeO₃–0.3BaTiO₃ (x = 0, 0.01, 0.03, 0.05, 0.07) ceramics are synthesized using a sol–gel method combined with two-step sintering. The effects of La content on phase structure, defect chemistry, and dielectric, ferroelectric, and strain properties are systematically investigated. The results show that La³⁺ doping effectively suppresses Bi³⁺ volatilization, thereby reducing the concentrations of oxygen vacancies and Fe²⁺. The sample with x = 0.03 exhibits the lowest leakage current density together with the highest remanent polarization (P_r = 33.53 µC cm⁻²). When the doping level increases to x = 0.05, the system approaches a rhombohedral-pseudocubic morphotropic phase boundary (MPB). Consequently, the dielectric constant, strain response, and equivalent piezoelectric coefficient (297 pm V⁻¹) all reach their maximum values, while the coercive field decreases to a minimum (E_c = 22.2 kV cm⁻¹). However, excessive doping (x = 0.07) increases the defect concentration again, alters the phase structure, and leads to the deterioration of all the aforementioned properties. This work provides clear compositional guidelines for selectively optimizing different functional properties of the material through a single dopant.