Structure and electrical properties of the Ho₂O₃ doped 0.82Bi_0.5Na_0.5TiO₃–0.18Bi_0.5K_0.5TiO₃ lead-free piezoelectric ceramics

Ho₂O₃ (0–0.7 wt%)-doped 0.82Bi_0.5Na_0.5TiO₃–0.18Bi_0.5K_0.5TiO₃ (BNKT18) lead-free piezoelectric ceramics were synthesized by a conventional solid-state reaction method. The effects of Ho₂O₃ on the microstructure and electrical properties were investigated. X-ray diffraction data shows that Ho₂O₃ in an amount of 0.1–0.7 wt% can diffuse into the lattice of the BNKT18 ceramics and form the pure perovskite phase. Scanning electron microscope (SEM) images indicate that the grain sizes of BNKT18 ceramics decrease with the increase of Ho₂O₃ content; in addition, the modified ceramics have the clear grain boundary and a uniformly distributed grain size. At room temperature, the electrical properties of the BNKT18 ceramics have been improved with the addition of Ho₂O₃, and the BNKT18 ceramics doped with 0.3wt.% Ho₂O₃ have the highest piezoelectric constant (d ₃₃ = 137 pC/N), the highest remnant polarization (P _r = 26.9 μC/cm²), the higher relative dielectric constant (ε _r = 980) and lower dissipation factor (tanδ = 0.046) at a frequency of 10 kHz. The BNKT18 ceramics doped with 0.1 wt% Ho₂O₃ have the highest planar coupling factor (k _p = 0.2426).