Large Electrostrain and High Optical Transmittance via Oxygen Octahedron Rotation Disordering in KNN Ceramics.

Lead-free K0.5Na0.5NbO3 (KNN)-based ceramics are promising candidates for multifunctional electronic materials. Nevertheless, the synergistic optimization of electrostrain and optical transmittance in KNN polycrystalline ceramics remains a critical challenge, owing to the structural trade-off between large strain and high transparency. Here, we employ chemical disorder engineering specifically through BaTiO3 (BT) substitution to manipulate the BO6 oxygen octahedron rotation disorder. BT incorporated into KNN gradually modulates the BO6 rotation mode from local ordering to a random distribution, which refines the size of cubic-phase-enriched polar nanoregions, facilitating high transparency in visible-light range. The disordered BO6 rotation essentially lowers the thermodynamic switching barriers for polarization and strengthens the defect-dipole pinning effect, thereby enhance the electrostrain synergistically. The optimal composition, i.e., KNN-0.03BT exhibits a large electrostrain of 1.2% and an optical transmittance of 60% in visible-light range. By overcoming the long-standing bottleneck in traditional polycrystalline ceramics, this work elucidates the core mechanism of atomic-scale disordering-enhanced polarization response and reduced optical loss, thereby advancing multifunctional material applications such as transparent sensing and flexible electronics.