Effect of Ln2O3 (Ln = La, Pr, Eu, Gd) addition on structure and electrical properties of (Na0.5Bi0.5)0.93Ba0.07TiO3 ceramics

(Na0.5Bi0.5)0.93Ba0.07TiO3 ceramics added with 0.2 wt.% Ln2O3 (Ln = La, Pr, Eu, Gd) were prepared by a citrate method, and the structure and electrical properties of the ceramics were investigated with respect to the size of the lanthanide. All the specimens maintain a coexistence of rhombohedral and tetragonal phases in crystal structure, while no remarkable evolution in microstructure with the lanthanide addition was observed. Compared with (Na0.5Bi0.5)0.93Ba0.07TiO3, the lanthanide addition resulted in an increased diffuseness in phase transition and a decrease in depolarization temperature (Td). The variation in dielectric, piezoelectric and ferroelectric properties with the lanthanide addition presents an evident lanthanide size dependence. The addition of La2O3 or Pr2O3 tailored the electrical properties basically following a soft doping effect, with the specimens added with La2O3 and Pr2O3 attaining high piezoelectric constants (d33) of 188 and 184 pC/N, respectively. By contrast, the Eu2O3 or Gd2O3 addition led to an abnormal change in the electrical properties, which was qualitatively interpreted by an internal stress effect.