Second‐order‐transition like characteristic contributes to strain temperature stability in (K, Na)NbO3‐based materials

Abstract

AbstractHigh strain and good temperature stability are contradictory properties in (K, Na)NbO3 (KNN)‐based materials. Herein, good temperature stability with high strain is obtained in a multiphase coexistent [ie, orthorhombic‐tetragonal (O‐T) and rhombohedral‐orthorhombic‐tetragonal (R‐O‐T)] KNN. A second‐order transition‐like characteristic should contribute to the temperature stability, in which an intrinsic lattice structure forms a bridge between them. The observed second‐order transition‐like characteristic is due to the reduced discrepancy among different lattice symmetries and a broadened temperature region for the phase transition. These integrated factors can slow the latent heat in a first‐order transition and extend it over a wide temperature region, thereby exhibiting second‐order transition‐like behavior. Correspondingly, the abrupt increase in strain near the phase transition temperature significantly slows. In addition, the appearance of pure tetragonal symmetry (P4mm) is deferred to a much higher temperature than TO‐T, in which the strain will inevitably decrease. As a result, good temperature stability with a high strain response can be realized in multiphase coexistent KNN materials, including d33*=448 pm/V, ‐27.5%≤fluctuation≤4.2% for O‐T, and d33*=446 pm/V, ‐17.5%≤fluctuation≤7.6% for R‐O‐T, over the whole temperature range 25 °C‐190 °C.