Conduction mechanism of donor and acceptor doped sodium niobate-based ceramics

Recently, NaNbO3 (NN) has become a hot topic of current research due to its antiferroelectric energy storage properties, which demand that the ceramics withstand large applied electric fields. The breakdown strength is dependent on conduction properties, but there is limited research on the conduction mechanisms of NN. Here we report that A-site donor-doping of Bi3+ (BixNa1-3xNbO3) and B-site acceptor-doping of Mg2+ (NaNb1-2/5yMgyO3) in NN lead to dramatic changes in the magnitude of the bulk conductivity (ab) and the conduction mechanism of NN ceramics. Undoped NN exhibits mixed conduction behavior with an oxide ion transport number (tion) of -0.44, and ab of -10-6 S/cm at 600 degrees C. A low level of Bi3+ doping (x = 0.06) suppresses the NN mixed conduction mechanism to electron conduction (tion - 0), and the bulk conductivity increases significantly, ab > 10-4 S/cm at 600 degrees C. On the other hand, Mg2+ doping (y = 0.06) samples mainly change the ab, with the mixed ion/hole conduction (tion - 0.43) and ab > 10-4 S/cm at 700 degrees C. The results show that the conductivity of NN increases and exhibits different conduction mechanisms with the doping of Bi3+ and Mg2+. Aliovalent doping is not beneficial to improving the insulation properties. Thus, this work provides theoretical guidance for the study of energy storage characteristics and the suppression of leakage behavior of high-temperature dielectric capacitors.