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

0.95(Li0.02Na0.50K0.48)(Nb0.95Sb0.05)O-3-0.05AgTaO(3) (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 T-1 sintering temperature and t(1) holding time in the first stage of the TSS, the relative permittivity of the 0.95LNKNS-0.05AT ceramics sintered at 1140 degrees C for 0.5 h and 1050 degrees 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 d(33), g(33), and K-p values are increased from 134 pC/N, 14.6 x 10(-3) Vm/N, and 17.4% to 224 pC/N, 25.5 x 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.