In situ mapping of {100}_pc residual strains in NaNbO₃ across thermally induced phase transitions

Realizing optimized functional properties in electroceramics relies on engineering their microstructures from micro to nanoscales. In the context of lead-free antiferroelectric materials, the balance involving the coexistence of the antiferroelectric-ferroelectric polymorphs at room temperature plays a crucial role on the development of the next generation on devices. In this way, rational microstructure control is essential to prevent efficiency losses and irreversibility of its characteristic double hysteresis loops. However, the current mechanistic understanding of the defect-tuned energy storage functionalities in these materials is challenged by the complex lattice dynamics and hierarchical morphology. Consequently, the extrinsic and intrinsic bulk’s behavior lacks a comprehensive understanding due to the lack of experimental techniques capable of probing features embedded in them. To overcome such a limitation, we investigate the structure-property relationship of antiferroelectrics by Dark-field X-ray microscopy. This new synchrotron technique enables a high-resolution visualization of domains, grain distribution, and strains within the bulk. In this work, we focus on the interplay between crystal structure, strain, and grain morphologies in NaNbO₃. We investigated the sequential in situ evolution of {100}_pc grains across six phase transitions: from the paraelectric Pm-3m at high-temperature towards the antiferroelectric Pbcm at room-temperature. The results are discussed in terms of residual strain and orientation distributions for all the present phases.