A new concept to enhance piezoelectricity and temperature stability in KNN ceramics

To relieve the sensitivity of piezoelectric coefficient (d33) to composition and strengthen temperature stability of strain in potassium sodium niobate {(K, Na)NbO3, KNN} ceramics, we proposed a new concept, tuning the trade-off between long-range ordering (LRO) and polar nanoregions (PNRs), and realized it by tailoring the content of bismuth (Bi) in an already-constructed multiphase coexistence, namely, 0.96(K0.48Na0.52)(Nb0.955Sb0.045)O3-0.04(BixNa4-3x)0.5ZrO3-0.3 mol%Fe2O3 ceramics. We obtained not only the high retention of > 83% at x = 0.80–1.10 in d33 but also higher d33 at x = 0.90–0.95, relieving the sensitivity of d33 to composition. We also obtained not only the enhanced strain but also the high retention of ≥ 79% over a wide temperature range of 20–180 °C at x = 1.10, irrespective of the electric field, strengthening the temperature stability. We demonstrated that high d33 values hinge on the trade-off between LRO and PNRs, and the enhanced temperature stability of strain originates from the diffused multiphase coexistence and the reduced contribution of domain switching. Therefore, the new concept helps further design high-performance KNN-based ceramics for practical application.