Giant strain vanishes in multilayer ceramics: The limitation of defect-dipole engineering

The introduction of oxygen vacancies and defect dipoles to induce giant bending strain is a cutting-edge strategy to improve the performance of piezoelectric ceramics. However, its feasibility in a more widely used multi-layer structure is still unknown. In this study, it is found that the giant strain successfully achieved in single-layer ceramics almost disappeared in multi-layer ceramics based on the same material system. The system analysis shows that the internal mechanical clamping effect introduced by the multi-layer structure and the opposite bending direction between adjacent layers are the root causes of large strain failure. The conclusion of this study clearly points out that the excellent piezoelectric properties in unconstrained single-layer samples cannot be directly converted into the actual advantages of multi-layer devices. This finding provides a crucial application perspective correction for the current popular defect engineering research.