Time dependence of domain structures in potassium sodium niobate-based piezoelectric ceramics

Piezoelectric materials, which can convert energy between electrical and mechanical forms, are widely used in modern industry. (K,Na)NbO3-based ceramics have attracted extensive attention due to their excellent performance characteristics among the lead-free materials. Piezoelectric properties are closely related to ferroelectric domain structures including the domain morphology and domain wall motion. However, time dependence of ferroelectric domains in (K,Na)NbO3-based ceramics has barely been studied. Here, we synthesized Li-doped KNN ceramics. The morphologies and crystallographic parameters of the domain structures were characterized. Two ferroelectric domains, the 60 degrees/120 degrees and 180 degrees domains, were identified in the ceramic. Surprisingly, the domain structure changed naturally as time passed, and most of the change occurred in the 180 degrees domain wall, while the 60 degrees/120 degrees domains remained nearly unchanged. Our results are different from those of previous studies, which showed that the non-180 degrees domain wall was more prone to movement than the 180 degrees domain wall.