Decoding the Piezo-Contributions of Potassium Sodium Niobate Ceramics

The contributions to the piezoelectric coefficient d33 from the intrinsic contribution, reversible low-field domain wall vibration, and irreversible domain switching and displacement of domain walls have been quantitatively investigated in potassium sodium niobate (KNN) ceramics with different phase structures. By measuring the piezoelectric coefficient at a large field and the piezoelectric hysteresis under subswitching conditions following Rayleigh relations, the intrinsic/extrinsic and reversible/irreversible piezoelectric responses are studied to understand the role of different phase boundaries in enhancing the piezoelectricity. This lattice contribution, reversible domain wall vibration, and irreversible contributions are strongly dependent on the crystal and domain structures of the examined ceramics. The intrinsic, reversible extrinsic, and irreversible extrinsic piezoelectric coefficients can both be enhanced in the phase instability regime for KNN-based ceramics. With respect to the intrinsic piezoelectric contribution ratio, ceramics with an orthorhombic-tetragonal (O-T) region have larger values as compared with those having orthorhombic (O)/rhombohedral-orthorhombic-tetragonal (R-O-T)/rhombohedral-tetragonal (R-T) regions. For KNN ceramics, the extrinsic piezoelectric response is the major contributor to the high piezoelectricity. Strongly linked to temperature, the intrinsic contributions of O/O-T/R-O-T phases decrease first and then increase near the phase transition temperature of the O phase to the T phase in the temperature range, with an opposite tendency in R-T phases.