Structure and electrical properties of Er2O3 doped 0.82Bi0.5Na0.5TiO3–0.18Bi0.5K0.5TiO3 lead-free piezoelectric ceramics

Er2O3 (0–0.8 wt.%)-doped 0.82Bi0.5Na0.5TiO3–0.18Bi0.5K0.5TiO3 (BNKT18) lead-free piezoelectric ceramics were synthesized by a conventional solid-state reaction method. The effects of Er2O3 on the microstructure and electrical properties were investigated. X-ray diffraction (XRD) data shows that Er2O3 in an amount of 0.2–0.8 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 Er2O3 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 Er2O3, and the BNKT18 ceramics doped with 0.6 wt.% Er2O3 have the highest piezoelectric constant (d33 = 138 pC/N), the highest planar coupling factor (kp = 0.2382), the highest remnant polarization (Pr = 25.2 μC/cm2), the higher relative dielectric constant (εr = 936) and lower dissipation factor (tanδ = 0.047) at a frequency of 10 kHz. Moreover, the Tm and Td of the samples increase with the addition of Er2O3.