The correlation between the microstructure and macroscopic properties of (K,Na,Li)(Nb,Ta)O₃ ceramic via rare earth oxide doping

Li_0.05(Na_0.51K_0.49)_0.95(Nb _0.95Ta_0.05)O₃ (abbreviated as KNNLT) with addition of La₂O₃, CeO₂, respectively, were prepared by a conventional ceramic fabrication technique. X-ray diffraction pattern shows that the coexistence of orthorhombic and tetragonal phase structure for KNNLT was not changed by adding La₂O₃ or CeO₂. SEM observation indicates that these two kind dopants have a remarkable effect on the microstructure of KNNLT ceramics. The T_o-t (temperature for the orthorhombic to tetragonal phase) was shifted toward lower temperature by the addition of rare earth oxide and typical relaxor ferroelectric is demonstrated especially for KNNLT with high content of La ₂O₃. An addition of 0.5% CeO₂ could strengthen the piezoelectric and dielectric constant of KNNLT ceramics to some extent. KNNLT ceramics with 0.5% CeO₂ obtain optimum electrical properties: d₃₃=272 pC/N, k_p=45%, ε_r=784 and tan δ=1.4%.