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 - x Bi(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 Amm 2 to cubic Pm 3̄ m 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.