The effect of B-site substitution on the structural evolution and electrical properties of lead-free (K,Na)NbO3 ceramics

Lead-free (K0.49Na0.51)(Nb1−xSbx)O3 piezoelectric ceramics were prepared via the conventional sintering method and the effect of the substitution of Nb with Sb on the phase structure, microstructure and electrical properties of the prepared (K0.49Na0.51)(Nb1−xSbx)O3 ceramics was systematically investigated. The prepared ceramics exhibited a single-phase perovskite structure which changed from a standard orthorhombic structure to a pseudocubic structure as x was increased from 0 to 0.1. X-ray diffraction patterns and Raman spectra obtained for the prepared ceramics clearly revealed that the degree of structural symmetry increased with x. Substituting an appropriate amount of Sb5+ for Nb5+ was found to improve the microstructure and thereby enhance the piezoelectric/ferroelectric properties. Further increasing the Sb content resulted in a decrease of the average grain size and a deterioration of the performance. The peak values of the piezoelectric constant d33 (182 pC/N) and the electromechanical coupling coefficient kp (41%) were obtained for the ceramic with x=0.06.