Enhanced Thermal Stability and Fatigue Characteristics in KNN-Based Relaxation Ferroelectrics through Nonstoichiometric Doping of Ta ⁵⁺

In order to improve the properties of potassium sodium niobate ceramics and achieve their application in fields such as actuators and resonators as soon as possible, this study developed a nonstoichiometric Ta-doped KNN ceramic system, which not only enhances the piezoelectric performance but also improves the thermal stability and fatigue cycling characteristics. The optimal d 33 * value of the sample with an excess Ta content of 3 mol % was 415 pm/V. Compared to its performance at room temperature, the d 33 * value of the sample with x = 0.03 decreased by 8.7% at 120 °C, demonstrating better thermal stability than other compositions. Moreover, after 10 6 ferroelectric cycles, its P max increased by 16.12%, demonstrating superior performance. The excess Ta doping effectively stabilizes the multiphase coexistence in KNN ceramics, promotes domain refinement, enhances relaxor characteristics, and reduces polarization at the doping sites, thereby significantly improving the material’s thermal stability and fatigue cycling characteristics.