Ultra‐Low Dielectric Loss and High Depolarization Temperature Achieved in (K,Na)NbO ₃ ‐Based Piezoceramics via Modulating Carrier Migration and Domain Dynamics

ABSTRACT The operational efficiency and reliability of lead‐free piezoceramics are critically limited by high dielectric loss and inadequate thermal stability. While enhancements in piezoelectricity have been achieved in (K,Na)NbO ₃ (KNN)‐based systems, a significant challenge remains: the effective co‐regulation of these two properties, as higher piezoelectricity often leads to increased dielectric loss and deteriorate thermal stability. This work presents a strategic solution which synergistically regulates carrier migration, and domain dynamics via defect engineering. In 0.3mol% CuO‐doped KNN‐based piezoceramics, we achieve an unprecedented ultra‐low dielectric loss of 0.3%, a superior piezoelectric coefficient ( d ₃₃ ) of 264 pC/N, high depolarization temperature ( T _d ) of 285°C, as well as excellent thermal‐aging and long‐term aging stability. Mechanistic studies reveal that the low loss originates from suppressed polarization switching and domain‐wall motion induced by oxygen vacancies, coupled with low ionic conductivity. While in situ heating transmission electron microscopy analysis shows that a stable hierarchical domain architecture underpins the superior piezoelectric thermal properties. This work establishes a new paradigm for designing lead‐free piezoceramics that simultaneously overcome the long‐standing challenges of dielectric loss and high depolarization temperature, paving the way for achieving highly efficient and reliable piezoelectric systems.