Effects of Eu2O3 on the structure and electrical properties of 0.82Bi0.5Na0.5TiO3–0.18Bi0.5K0.5TiO3 lead-free piezoelectric ceramics

Eu2O3 (0–0.8 wt.%)-doped 0.82Bi0.5Na0.5TiO3–0.18Bi0.5K0.5TiO3 (BNKT18) lead-free piezoelectric ceramics were synthesized by conventional solid-state processes. The compositional dependence of phase structure and electrical properties of the BNKT18 ceramics was studied. X-ray diffraction (XRD) data shows that 0.2–0.8 wt.% Eu2O3 has diffused into the lattice of BNKT18 ceramics and forms a pure perovskite phase. SEM images indicate that the grain size of BNKT18 ceramics decreases with the increase of Eu2O3 content, and all the modified ceramics have a clear grain boundary and a uniformly distributed grain size. At room temperature, the ferroelectric and piezoelectric properties of the BNKT18 ceramics have been improved with the addition of Eu2O3, and the BNKT18 ceramics doped with 0.4 wt.% Eu2O3 have the highest piezoelectric constant (d33 = 145 pC/N), highest relative dielectric constant (εr = 1134) and lower dissipation factor (tan δ = 0.045) at a frequency of 10 kHz. The BNKT18 ceramics doped with 0.2 wt.% Eu2O3 have the highest planar coupling factor (kp = 0.251). The temperature dependence of the relative dielectric constant shows Tm increases with the addition of Eu2O3.