Continuous Phase Transition Enables Piezoelectric Thermal Stability in KNN-Based Multilayer Textured Ceramics

Overcoming the trade-off between multiphase coexistence and phase transformation in piezoelectrics remains a critical challenge for achieving high and stable piezoelectric performance over a broad temperature range. Here, we resolve this long-standing dilemma by constructing a continuous phase transition through multilayer ceramic texture engineering. Specifically, two types of (K,Na)NbO₃-based piezoelectric ceramics with distinct polymorphic phase boundary (PPB) features are physically composed. The composite ceramics exhibit hierarchic phase and domain structures, particularly a continuous phase transition, enabling outstanding piezoelectric performance and thermal stability across a wide temperature range. As a result, the multilayer composite ceramics prepared in this work demonstrate excellent room-temperature piezoelectric properties, with a piezoelectric coefficient (d₃₃) ∼ 420 pC N^-1 and an inverse piezoelectric coefficient (d₃₃*) ∼ 600 pm V^-1. More importantly, within the temperature range of 25°C-100°C, the variation in d₃₃ and d₃₃* values is merely 2%. This work establishes a continuous phase transition-driven paradigm for enhancing piezoelectric thermal stability, demonstrating universal potential to decouple the constraints imposed by multiphase coexistence and phase transformation in next-generation piezoelectric materials.