Effects of Bi(Zn_0.5Ti_0.5)O₃ introduction on the structures and electrical properties of BiFeO₃–BaTiO₃ lead-free piezoelectric ceramics

The binary perovskite-type compound (1 − x)BiFeO₃–xBaTiO₃ (BF-BT) is considered as a promising high-temperature lead-free piezoelectric material due to its high Curie temperature (T_C > 400 °C) and better electromechanical properties. In this work, ternary lead-free piezoelectric ceramics with a chemical formula of (0.67 − x)BiFeO3–0.33BaTiO3–xBi(Zn0.5Ti0.5)O₃ + 1 mol% MnO₂ (where x = 0–0.05) were prepared by the conventional solid-state reaction route. The effects of Bi(Zn_0.5Ti_0.5)O₃ introduction on the phase structures and microstructures, piezoelectric and dielectric properties, as well as impedance characteristics of BF-BT ceramics were investigated in detail. Firstly, all the samples synthesized exhibit a pure perovskite structure with the coexistence of rhombohedral (R) and tetragonal (T) phases, and the T phase content increases with increase in x. A small amount of Bi(Zn_0.5Ti_0.5)O₃ (x ≤ 0.03) that were incorporated into the perovskite lattice of BF-BT can promote the grain growth of ceramics. Secondly, all samples were found with a notable relaxed phase transition behavior, T_C of the system decreases with increase in x. The AC impedance spectra of the samples were fitted and analyzed according to the R-CPE equivalent circuit model, the electric impedance of the ceramics at high temperatures was mainly contributed by grain boundaries. Moreover, the dielectric relaxation activation energy of the samples firstly decreases and then increases with increase in x. Finally, the composition with x = 0.02 shows the optimized electrical properties among these samples, including T_C = 454 °C, d₃₃ = 117 pC/N, k_p = 23%, tanδ = 0.11, which are mainly benefited from the bismuth content compensation and the substitution of (Zn_0.5Ti_0.5)³⁺ for Fe³⁺ at B-site reducing the valence change of Fe³⁺ in BF-BT.