One simple approach, two remarkable enhancements: Manipulating defect dipoles and local stress of (K, Na)NbO3-based ceramics

Although the composition-driven multi-phase coexistence strategy has been widely used to modify the piezoelectric properties of potassium sodium niobate ((K, Na)NbO3, KNN) based ceramics, the trade-off between long-range ferroelectric ordering and chemical additives-induced disorder hinders the further improvement of piezoelectricity and makes the electric field-induced strain temperature-dependent. Herein, to resolve two issues, we proposed a new concept, that is, manipulating defect dipoles and local stress of a pre-constructed multi-phase coexistence through controlling zirconium (Zr) content. We validated the new concept by designing 0.96(K0.4Na0.6)Nb0.955Sb0.045O3-0.04(Bi0.5Na0.5)Zr(1+x)O3 ceramics. In samples with Zr deficiency (i.e., x=-0.1), we obtained high retention of 91% in normalized unipolar strain (Suni) over the temperature range of 30-160 °C, even under low electric fields of 10-20 kV/cm, superior to those of other representative KNN-based ceramics. In samples with slight Zr excess (i.e., x=0.07), we achieved an increase in direct piezoelectric coefficient (d33) and converse piezoelectric coefficient (d33*) by 12% and 25%, respectively, in comparison with that at x=0. The enhanced temperature stability stems from the released domain walls that are pinned by defect dipoles, and the increased d33 (and d33*) originates from the synergetic contributions of the multi-phase coexistence, increased grain size, and stabilization of the ZrO2 secondary phase. Therefore, our new concept would benefit the composition design and performance improvement of KNN-based ceramics in the future.