Lead-free ceramics based on the (1 − x)K 0.5Na 0.5NbO 3– xBi(Zn 0.5Ti 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 0.5Ti 0.5)O 3 substitutions up to 30 mol%. The crystal structure was found to transform from orthorhombic Amm2 to cubic Pm3̄ m through mixed rhombohedral and tetragonal phases with the increase in Bi(Zn 0.5Ti 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 0.5Na 0.5NbO 3)–0.02(BiZn 0.5Ti 0.5O 3) showed an improved room temperature piezoelectric coefficient d 33 = 109 pC/N and a high Curie temperature T C = 383 °C.
Room temperature powder X-ray diffraction patterns of (1 – x)K 0.5Na 0.5NbO 3– xBi(Zn 0.5Ti 0.5)O 3 system.