Microstructure and impedance properties of La, Ce multi-rare earth ions doped Na0.5Bi2.5Nb2O9 Aurivillius type ceramics

(Li, Ce, La) multi-doped Na0.5Bi2.5Nb2O9 ceramics were prepared by a conventional solid state sintering method. Microstructure of sintered ceramics was examined by the X-ray diffraction and scanning electron microscopy. The introduction of voluminous La3+ cations decreases the degree of lattice distortion, leading a lower Curie-temperature. The detailed electrical conduction behaviors were determined by the electrochemical impedance spectra (EIS). The electrical properties were investigated as a function of frequency (102-106 Hz) at various temperatures (350-750 °C). The underlying physical mechanism of electrical properties at high temperature for multi-rare-earth doping NBN-based was studied via an assistance of EIS techniques. There were a set of Debye-like relaxation peaks in the imaginary part of impedance and electric modulus data. Oxygen vacancies are responsible for both ac conduction and dielectric relaxation processes. A discontinuous variation of the exponent parameter n is found owing to a ferroelectric-ferroelastic phase transition around 550 °C.