Effect of Ta Content on Phase Structure and Electrical Properties of Piezoelectric Lead‐Free [(Na 0.535 K 0.480 ) 0.942 Li 0.058 ](Nb 1− x Ta x )O 3 Ceramics

The Li/Ta‐codoped lead‐free (Na,K)NbO 3 ceramics with Na:K ratio of 0.535:0.480 were prepared by normal sintering, whose nominal formula was noted as [(Na 0.535 K 0.480 ) 0.942 Li 0.058 ](Nb 1− x Ta x )O 3 ( x =2, 4, 6, 8, 10, 12, 14, and 16 at.%). The X‐ray diffraction patterns and the corresponding calculation of lattice parameters showed that a morphotropic phase boundary crossing orthorhombic and tetragonal symmetries occurs at the compositions containing 6∼8 at.% Ta. Because of such transitional behavior achieved by optimizing Ta content, the piezoelectric coefficient ( d 33 ), electromechanical coupling coefficient ( k p ), and dielectric constant (ɛ) were enhanced to peak values, 232 pC/N, 39.4%, and 710, respectively. However, the Curie temperature ( T C ) and remanent polarization ( P r ) show a decreasing tendency with raising Ta content, and their maximum values are 462°C and 8.73 μC/cm 2 , respectively.