Influence of Compensated Li Content on Microstructure, Crystalline Phase and Electrical Properties of NKN-based Lead-free Piezoelectric Ceramics

High dense Li0.05+x(Na0.535K0.48)0.95NbO3 (LxNKN) lead-free piezoelectric ceramics with fine morphology were synthesised by conventional mixed-oxide method at 1000°C, and its microstructure, phase structure and electrical properties were investigated as a function of excessive Li addition. The results revealed that the excess Li content facilitated the sinterability and improved the piezoelectric properties for LxNKN ceramics. A PPT bridging tetragonal and orthorhombic symmetry was found at x= 0.01−0.015 by using the X-ray diffraction patterns and the corresponding calculation of lattice parameters. Owing to such transitional behavior, the piezoelectric coefficient (d33), electromechanical coupling coefficient (kp), dielectric constant (er) and remanent polarization (Pr) were enhanced to peak values, 282 pC/N, 44%, 942 and 27 μC/cm, respectively. Compared with LNKN ceramics, the variation in Curie temperature (Tc) by the compensation amount of Li was much smaller for LxNKN ceramics. The reason is that the amount of Li that entered into crystal lattice is relatively rare for LxNKN ceramics. The results provide a way to low-temperature sintering of LNKN-based lead-free piezoceramics with high performance.