(Bi_0.5Na_0.5)(Zr_0.97W_0.01Fe0.02)O₃ doping effects on KNN-based lead-free ceramics prepared via two-step sintering technique

(1-x)(Li0.02Na0.5K0.48)(Nb0.95Sb0.05)O-3-x(Bi0.5Na0.5)(Zr0.97W0.01Fe0.02)O-3 (LNKNbS-xBiNZWF, x = 0.035, 0.04, 0.045, 0.05, and 0.055) lead-free piezoceramics were fabricated by traditional solid-state sintering method via two-step sintering technique, where the effects of BiNZWF doping amount and ceramic processing were studied systematically. The formation of orthorhombic-tetragonal (O-T) phase boundary in the LNKNbS-xBiNZWF system is confirmed by X-ray diffraction Rietveld refinement and Raman spectroscopy, where the BiNZWF doping amount affects the O-T phase proportion. The LNKNbS-xBiNZWF ceramics approach to normal ferroelectrics but have apparent relaxation characteristic. Oxygen vacancies dominate the high-temperature conduction in the LNKNbS-0.04BiNZWF ceramics, which are generated by the volatilization of Bi and alkali metals during sintering. The LNKNbS-0.04BiNZWF ceramics exhibit excellent electrical properties, correlating with using the two-step sintering method, appropriate proportion of O phase and T phase, high densification and improved microstructure uniformity.