Simultaneous enhancement of piezoelectricity and Curie temperature in KNN-based ceramics via a multiple formula solid solution

Abstract

The development of lead-free, KNN-based piezoceramics with excellent comprehensive electrical properties is crucial for replacing commercial lead-containing counterparts and achieving an environmentally sustainable society. Although the proposed phase boundary engineering and local structure design can effectively improve the piezoelectric coefficients (d₃₃) of KNN-based ceramics, the difficulty in achieving saturated poling and the inevitable requirement of sacrificing the Curie temperature (T_C) are urgent issues that need to be addressed. Herein, we adopted a multiple formula solid-solution strategy that effectively overcomes the longstanding conflict between d₃₃ and T_C, which can be attributed to the balance between the well-maintained, long-range ferroelectric order and chaotic local disorder. This approach has resulted in superior comprehensive electrical properties for a KNN-based lead-free system, achieving a remarkable d₃₃ of 550 pC N⁻¹ and T_C of 260 °C, which significantly outperform previously reported values. This work provides a method to achieve KNN-based ceramics with excellent comprehensive electrical properties, which is expected to benefit numerous functional materials.