Attempt for excellent piezoelectric performance in Sb-free (K,Na) NbO₃-based ceramics

Piezoelectric temperature stability is often a very important item for piezoelectric materials when putting them into practical applications like filters and ultrasonic transducers. Phase transitions of (K,Na)NbO3-based compositions that contain neither toxic Pb nor Sb elements were tailored to simultaneously acquire enhanced piezoelectric properties and good piezoelectric temperature stability in this study. Specifically, dense 0.94 (K0.48Na0.52)NbO3-0.03BaZrO3-0.01BaSnO3-0.02(Bi0.5Na0.5)ZrO3 ceramic and its further compositionally modified one by 1 wt% MnO2 were prepared. Both of these two ceramics display quite weak piezoelectric temperature dependence in the usage temperature range between -30 degrees C-100 degrees C, but the one modified by MnO2 has the significantly improved piezoelectric properties with a high piezoelectric coefficient d33 of 310 pC/N and large electromechanical coupling factors kp and k33 of 0.57 and 0.73 at room temperature. The obtained excellent piezoelectric performance is considered to be associated closely with the stable piezoelectric characteristic of the orthorhombic phase and the diffused rhombohedral-orthorhombic and orthorhombic-tetragonal phase transitions.