Harnessing the synergistic effects between a polymorphic phase boundary and second-phase hardening for enhanced electromechanical compatibility in KNN-based ceramics

Abstract

Achieving both a high piezoelectric coefficient (d₃₃) and mechanical quality factor (Q_m) is essential for high-power piezoelectric applications, yet their inherent trade-off remains a longstanding challenge. Here, we demonstrate a strategy to balance these properties in 0.988 [0.957(K_0.48Na_0.52)Nb_0.95Ta_0.06O₃–x(Bi_0.5Na_0.5)ZrO₃–0.003BiFeO₃] + 0.012CuSb₂O₆ ceramics by synergistically coupling polymorphic phase boundary (PPB) engineering with second-phase ferroelectric hardening. The hardening effect, induced by residual thermal stresses and local electric fields, pins domain wall motion and switching to enhance Q_m. Concurrently, enriching the tetragonal phase within the orthorhombic–tetragonal phase boundary boosts the intrinsic piezoelectric contribution, which enhances polarization capability under nearly loss-free conditions and simultaneously improves both d₃₃ and Q_m. Additionally, the Zr⁴⁺ substitution for Nb⁵⁺ introduces oxygen vacancies and intensified lattice stress, further restricting domain dynamics and stabilizing Q_m. This multi-scale coupling strategy yields a breakthrough electromechanical compatibility, achieving d₃₃ = 240 pC N⁻¹ and Q_m = 500. These results provide a promising route to enhance the commercial feasibility of KNN-based ceramics, marking a significant advancement in developing high-performance, environmentally friendly piezoelectric materials.