Enhanced properties of KNLN–BZ lead-free piezoelectric ceramics via three-step sintering

In this work, 0.94(K0.48Na0.52)0.935Li0.065NbO3–0.06BaZrO3 (abbreviated as KNLN–0.06BZ) lead-free ceramics were prepared by conventional sintering (CS) and three-step sintering (TSS). The effects of sintering process on the microstructure and piezoelectric properties of ceramics were systematically studied. The result showed that, the ceramic prepared by TSS obtained higher density and better electrical properties compared to the ceramic prepared by CS. As we all know, the formation of defects will have a pinning effect on the domain switching. According to the results of impedance spectroscopy analysis, the ceramics prepared by TSS have fewer oxygen vacancies, which will make domain switching easier at an applied electric field, resulting in more excellent piezoelectric activity. The ceramics prepared by TSS with different sintering conditions showed different properties, but multiple phases may coexist in all ceramic samples according to the analysis of XRD, and the domain can adequately switch at an external electric field due to lower energy barrier at the phase boundary, resulting in high piezoelectric properties of ceramics. Hence, when the sintering condition was 1050 °C/0 min–1150 °C/5 min–1070 °C/20 h, the ceramic samples exhibited an optimal performance of ρ = 4.51 g/cm3, d33 ~ 258 pC/N, kp ~ 0.35, and TC ~ 328 oC. This superior result manifests that the KNLN–0.06BZ ceramic prepared by TSS is a promising ceramic for industrial application.