Effects of Bi₂O₃ additive on sintering process and dielectric, ferroelectric, and piezoelectric properties of (Ba_0.85Ca_0.15)(Zr_0.1Ti_0.9)O₃ lead-free piezoceramics

Lead-free Ba_0.85Ca_0.15Zr_0.1Ti_0.9O₃ (BCZT) piezoceramics with Bi₂O₃ additive were synthesized using solid-state ceramic processing. Various amounts of Bi₂O₃ (0.05, 0.1, 0.5, and 1.0 mol%) were added after calcination, milled, compacted, and sintered with no compensation at A- or B-sites. Addition of up to 0.5 mol% Bi₂O₃ was found to greatly enhance the densification and increase the piezoelectric properties, while higher amounts decreased the grain size and induced relaxor-like electrical behavior, obeying the Vogel-Fulcher model. The highest properties were obtained for the BCZT with 0.1 mol% Bi₂O₃ sintered at 1350 °C: d₃₃ = 325 pC/m, d₃₃^* = 509 pm/V (at 3 kV/mm), k_p = 0.42, and P_r = 10.4 μC/cm². The microstructure, phase composition, and local structure were investigated by scanning electron microscopy, X-ray diffraction, and Raman spectroscopy. The appearance of the A_1g vibration mode in the Raman spectra and the shift of diffraction peaks to lower 2θ values indicate the incorporation of Bi³⁺ into the B-site of the perovskite BCZT structure.