Tantalum influence on electrical properties of lead-free (K0.4425Na0.52Li0.0375)(Nb0.93−x Ta x Sb0.07) O3 piezoelectric ceramics

Abstract

Lead-free (K0.4425Na0.52Li0.0375)(Nb0.93−x Sb0.07Ta x )O3 (abbreviated as KNLNST x ) piezoelectric ceramics with x = 0.045–0.075 have been prepared by an ordinary sintering technique with sintering temperature at 1,120 °C. The results of X-ray diffraction reveal that Ta5+ has diffused into the perovskite lattice to form a solid solution. The grain growth of the ceramics was inhibited by substituting Ta5+ for Nb5+. It has been shown that the substitution of Ta decreases Curie temperature T C and orthorhombic-tetragonal phase transition temperature T O-T. Besides, the dependence of the ceramics with different Ta content on the dielectric, piezoelectric and ferroelectric properties has been investigated. The results indicate that Ta substitution provides “soft” piezoelectric characteristics, owing to improvements in d 33, k p and e r and a decease in Q m. For the ceramics with x = 0.06, the piezoelectric coefficient d 33 becomes maximum at a value of 270 pC/N, while the other electrical properties remain reasonably high: dielectric constant e r = 1,577, planar mode electromechanical coupling factors k p = 0.4, Curie temperature T C = 252 °C and the remanent polarization P r = 16.03 μC/cm2. These results show that (K, Na, Li) (Nb, Sb)O3 ceramics with small amount of Ta (x <8 mol%) are good lead-free piezoelectric ceramic.