Structure, dielectric, and piezoelectric properties of K(0.5)Na(0.5)NbO(3)-based lead-free ceramics

Lead-free ceramics based on the (1 − x)K(0.5)Na(0.5)NbO(3)–xBi(Zn(0.5)Ti(0.5))O(3) (KNN–BZT) system obtained via the conventional solid-state processing technique were characterized for their crystal structure, microstructure, and electrical properties. Rietveld analysis of X-ray diffraction data confirmed the formation of a stable perovskite phase for Bi(Zn(0.5)Ti(0.5))O(3) substitutions up to 30 mol%. The crystal structure was found to transform from orthorhombic Amm2 to cubic Pm3̄m through mixed rhombohedral and tetragonal phases with the increase in Bi(Zn(0.5)Ti(0.5))O(3) content. Temperature-dependent dielectric behavior indicated an increase in diffuseness of both orthorhombic to tetragonal and tetragonal to cubic phase transitions as well as a gradual shift towards room temperature. The sample with x ≈ 0.02 exhibited a mixed rhombohedral and orthorhombic phase at room temperature. A high-temperature X-ray diffraction study confirmed the strong temperature dependence of the phase coexistence. The sample with the composition 0.98(K(0.5)Na(0.5)NbO(3))–0.02(BiZn(0.5)Ti(0.5)O(3)) showed an improved room temperature piezoelectric coefficient d(33) = 109 pC/N and a high Curie temperature T(C) = 383 °C.