Excellent Electromechanical Compatibility in Alkaline Niobate Composite Achieved by Optimizing Internal Defects and Extrinsic Local Stress Field

Lead-free piezoelectric materials with excellent electromechanical compatibility are essential for industrial applications. However, attaining both a large piezoelectric coefficient ( d 33 ) and a high mechanical quality factor ( Q m ) is generally regarded as challenging because of the inherent trade-off among these properties. In this work, the reduction of internal defects and the redistribution of the second phase in potassium sodium niobate (KNN) based composite ceramics are achieved through a heat treatment technique. This method can achieve a significant improvement of electromechanical properties ( d 33 = 415 pC/N and Q m = 120), which effectively overcomes the contradiction between piezoelectric properties and mechanical losses. Structural characterizations indicated that the improved electromechanical performance of the annealed KNN composite ceramics could be attributed to the optimized internal defects and the extrinsic local stress field. These findings offer a promising route to enhance the commercial feasibility of lead-free KNN-based piezoelectric ceramics, representing significant progress in the development of high-performance and environmentally friendly piezoelectric materials.