Impact of stress-induced precipitate variant selection on anisotropic electrical properties of piezoceramics

Precipitation hardening has been recently validated as a new mechanism for domain wall pinning and mechanical loss reduction in piezoelectrics. While anisometric precipitates have high pinning strengths, there is limited knowledge about the electrical anisotropy of the precipitation-hardened piezoceramics. In the present work, we successfully orient the precipitates in Li_0.18Na_0.82NbO₃ piezoceramics by applying a uniaxial stress during the aging and studied its electrical anisotropy. Predicted by mechanical simulation and verified by transmission electron microscopy, it is demonstrated that the precipitate variant with its long axis perpendicular to the applied stress is energetically favored. The electrical anisotropy of the stress-assisted aged Li_0.18Na_0.82NbO₃ is studied by applying electrical fields parallel or perpendicular to the stress axis. The domain wall contribution to permittivity is found to vary by more than a factor of two depending on orientation. In addition, the domain walls are more difficult to be activated by increasing the temperature when the electric field is perpendicular to the stress axis. Our work highlights the precipitate variant selection induced by stress-assisted aging and the related electrical anisotropy in piezoceramics. This technique enables the precipitate orientation in piezoceramics and the utilization of its anisotropy, providing fundamental insight into precipitate-domain-wall interactions and setting the ground for leveraging precipitation hardening effect in piezoceramics.