Oxygen tracer diffusion analysis and observation of domain structure in quenched (Bi0.5Na0.5)TiO3 ceramics

Lead-free ferroelectric and piezoelectric ceramics, (Bi0.5Na0.5)TiO3 [BNT] ceramics were prepared by controlling the quenching rate. The quenching effects mainly caused an increase in lattice distortion 90-α and Td, contribution of electrical properties and ordered structural phase transitions. In this study, we analyzed oxygen tracer diffusion and examined domain structures for quenched BNT ceramics, and then we proposed a mechanism for the quenching effect. As a result, the diffusion coefficients D of 18O tracer for the OF and quenched samples were 2.5 × 10–11 and 1.8 × 10–11 cm2 s−1, respectively, and there were no significant differences in oxygen vacancies after quenching. The correlation between the quenching effect and oxygen vacancies was also examined in BNT with hard and soft dopants. However, the contribution of oxygen vacancies was small thus, the correlation between the quench effect and oxygen vacancies was low. On the other hand, the domain structure of BNT ceramics was observed and the domain size of OF-BNT was around 20 nm. This is a typical domain size for BNT ceramics. In contrast, the domain size of the quenched BNT was 40 nm. Thus, quenching increased the domain size and decreased their density. Consequently, we propose that the domain structure is strongly correlated with the quench-induced increase in lattice distortion and Td, its contribution to electrical properties, and ordered structural phase transitions.