Giant electrostrain coefficient under low driving electric field in sodium potassium niobate piezoelectric ceramics with symmetrical bipolar strain

Currently, achieving highly symmetrical bipolar strain and high electrostrain under low driving electric field remains challenging in piezoelectric materials. The designed potassium sodium niobate-based ceramics exhibit highly symmetrical bipolar strain and ultrahigh electrostrain coefficient (~2000 pm/V) under a low driving electric field of 8.4 kV/cm through A-site defect engineering and charge compensation. The highly symmetrical bipolar strain is related strongly to the lowly aligned defect dipoles by partially substituting A-site (Na⁺/K⁺) ions with Mn²⁺. The eye-catching performance is ascribed to the unique microstructure of atomic-scale polar nanoregions embedded in nano-domains (~34 nm) by tuning Na⁺/K⁺ ions deficiency and coexistence of multiple phases. Phase-field simulations reveal that flattened energy barrier and multiphase nanodomains interplay to boost electrostrain at low driving fields. This work provides an innovative way of designing lead-free piezoelectric materials with highly symmetrical bipolar strain and giant electrostrain coefficient at low driving electric field, promising for high-precision actuators applications.