Thermally stable piezoelectric properties of lead-free ceramics featuring polar topological domains

Environment-friendly lead-free piezoelectric materials with excellent piezoelectric characteristic and outstanding temperature stability play an important role in advanced functional applications. The past two decades have seen a great enhancement of piezoelectric coefficients (d₃₃) in (K, Na)NbO₃ based piezoceramics, but one notoriously unresolved issue is their severe temperature instability, obstructing them toward practical applications. This work proposes a novel strategy to optimize the thermal stability of KNN-based ceramics by constructing polar topological domains, which is driven by the competition between inhomogeneous polarization configuration in multiple symmetry phases accompanied by the local oxygen octahedral distortion, tilt and displacement. Thanks to the particular topological protection of polar topological domain with high density nanodomain walls, a superior temperature reliability (d₃₃ decreased only by 10 % in the temperature range of 25–120 °C) was realized, and the cantilever beam-type piezoelectric energy harvester assembled using the optimized sample displayed excellent high temperature power generation capacity, demonstrating that modulating polar topological domains is an effective avenue to develop new high-performance functional material for practical engineering applications.