Sinterability, crystal structure and piezoelectric properties of lead-free [Li0.06(Na0.52K0.48)0.94+x]NbO3 piezoelectric ceramics

Lead-free [Li0.06(Na0.52K0.48)0.94+x]NbO3 (hereafter L(NK)xN) piezoelectric ceramics were fabricated by normal sintering at 1020-1080 °C for 2 h. The crystal structure, microstructure and piezoelectrical properties were investigated with special emphasis on the influences of the alkali metal compensating content and sintering temperature. A polymorphic phase transition (hereafter PPT) from tetragonal to orthorhombic symmetry was identified by XRD analysis and the corresponding calculation of lattice parameters. Because of such transitional behavior achieved by optimizing compensating content x, the piezoelectric coefficient (d33), electromechanical coupling coefficient (kp), and dielectric constant (εr) were enhanced to peak values, 285 pC/N, 44.5% and 780, respectively. Both moderate compensating content and appropriate sintering temperature contribute to improve the relative density of the L(NK)xN ceramics. The relative density reaches its maximum value of 96% when the ceramic with x = 1.5 at.% was sintered at 1040 °C for 2 h.