Enhancing densification and electrical properties of KNN-based lead-free ceramics via two-step sintering

0.95(Li0.02Na0.50K0.48)(Nb0.95Sb0.05)O3-0.05AgTaO3 (0.95LNKNS-0.05AT) lead-free piezoelectric ceramics were prepared by conventional ceramic processing via the two-step sintering process (abbreviated as TSS). The influences of sintering conditions in the first stage of the TSS process on densification, dielectric and piezoelectric properties of the 0.95LNKNS-0.05AT ceramics prepared by the TSS were deeply studied. By introducing TSS for preparing the 0.95LNKNS-0.05AT ceramics, the volatilization of alkali metal elements can be decreased and all the 0.95LNKNS-0.05AT ceramics show high densification. By optimizing the T1 sintering temperature and t1 holding time in the first stage of the TSS, the relative permittivity of the 0.95LNKNS-0.05AT ceramics sintered at 1140 °C for 0.5 h and 1050 °C for 8 h is increased to 5957 at 1 kHz, while the relative permittivity of the 0.95LNKNS-0.05AT ceramics prepared by the conventional sintering method (abbreviated as CS) is only 5205. The d33, g33, and Kp values are increased from 134 pC/N, 14.6 × 10–3 Vm/N, and 17.4% to 224 pC/N, 25.5 × 10–3 Vm/N, and 31.9%, respectively. The 0.95LNKNS-0.05AT ceramics exhibit thermal activation relaxation behavior, and the high-temperature Cole–Cole impedance performance can be fitted well by the equivalent circuit (RQC) and equivalent circuit (RC) connected in series. The space charge effect conforms to the Arrhenius relationship, which presents a thermally activated hopping type process and relates to the oxygen vacancies generated by the evaporation of alkali metals during the TSS process.