Improving Piezoelectric Strain, Temperature Stability, and Strain Symmetry under a Low Driving Electric Field on KNN-Based Ceramics Sintered in a Reducing Atmosphere

The KNN-SZ + Zr + xMn ceramics prepared successfully in a reducing atmosphere show a high piezoelectric strain coefficient (d 33 *), high temperature stability of d 33 *, good bipolar strain symmetry, and high insulation resistance (1.42 x 1011 Omega.cm). Due to the occupying evolution of Mn ions, the concentration of defect dipoles ( M n N a / K . - V N a / K ' , M n N b ' - V O center dot center dot , and M n N b '' - V O center dot center dot ) increases at x = 5-8 and the concentration of defect dipoles ( M n N b ''' - V O center dot center dot ) increases at x = 6-8. The optimum piezoelectric strain coefficient (d 33 * = 623 pm/V at 10 kV/cm) of ceramics (x = 6) is attributed to the synergistic effect of enhanced spontaneous polarization (P S) extension and strong reversibility of rhombohedral-monoclinic phase transitions. The reduction in the oxygen vacancy (VO center dot center dot) concentration and formation of stable defect dipoles enable the ceramic (x = 6) to achieve a superior temperature stability in d 33 * (T 90 * = 160 degrees C). This study presents an important design to enhance synchronous piezoelectric strain, temperature stability, and bipolar strain symmetry of KNN-based ceramics sintered in a reducing atmosphere.