Li/Sb-doped (Na,K)NbO3 with a nominal composition of [Li0.05(Na0.535K0.48)0.95](Nb0.94Sb0.06)O3 ceramic was synthesized by normal sintering. The phase structure, microstructure, and electrical properties were investigated with a special emphasis on the influence of the sintering temperature. A polymorphic phase transition (PPT) from orthorhombic to tetragonal symmetry was observed when the sintering temperature was raised from 1040 to 1050 ℃, whereby the piezoelectric coefficient d33 and the electromechanical coupling coefficient kp reached the peak values of 245 pC·N-1 and 41.2%, respectively. The PPT induced by varying the sintering temperature is due to the different volatilization extents of alkali metals and appears to a lower sintering temperature with increasing Li content. The trace modifying of alkali metal content is more effective than doping B site element to enhance the d33 value.
ZnO-modified (Li, Na, K)NbO3 lead-free ceramics with a nominal composition of Li0.06(Na0.535K0.48)0.94NbO3+0.7mol% ZnO (LNKN-ZT) was synthesized normally at 930-1000℃. The Zn ions incorporated into the A-site at a higher sintering temperaVare, which changed LNKN-Z7 to soft piezoelectric ceramics with the mechanical quality factor decreasing from 228 to 192. A phase transition from tetragonal to orthorhombic symmetry was identified by XRD analysis, and the corresponding calculation of lattice parameters was conducted at 970-980℃. Because of such transitional behavior and fine microstructure, the optimized values of piezoelectric coefficient, planar electromechanical coupling coefficient, and relative dielectric constant were obtained.
