Structure, dielectric, and piezoelectric properties of K0.5Na0.5NbO3-based lead-free ceramics
Lead-free ceramics based on the (1 − x)K0.5Na0.5NbO3–xBi(Zn0.5Ti0.5)O3 (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(Zn0.5Ti0.5)O3 substitutions up to 30 mol%. The crystal structure was found to transform from orthorhombic Amm2 to cubic Pmm through mixed rhombohedral and tetragonal phases with the increase in Bi(Zn0.5Ti0.5)O3 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(K0.5Na0.5NbO3)–0.02(BiZn0.5Ti0.5O3) showed an improved room temperature piezoelectric coefficient d33 = 109 pC/N and a high Curie temperature TC = 383 °C.