Enhancement of piezoelectric properties of K0.5Na0.5NbO3-based ceramics by Ba(Li1/4Nb3/4)O3 addition

K0.5Na0.5NbO3(KNN)-based piezoelectric ceramics have been studied extensively because they are considered to be one of the most promising lead-free piezoelectric ceramics. The chemical modification of KNN-based ceramics by... [ view full abstract ]

K_0.5Na_0.5NbO₃(KNN)-based piezoelectric ceramics have been studied extensively because they are considered to be one of the most promising lead-free piezoelectric ceramics. The chemical modification of KNN-based ceramics by Li-containing perovskites is known to enhance the piezoelectric properties, resulting the presence of morphotropic phase boundary (MPB) between the orthorhombic and tetragonal phases. In this study, the (1-x)KNN-xBa(Li_1/4Nb_3/4)O₃ (BLN) ceramics were synthesized and the compositional dependence of piezoelectric properties was investigated.

The XRPD profiles of (1-x)KNN-xBLN ceramics sintered at the optimum temperatures for 3 h exhibited single phase in the composition range of 0 - 0.02; the peak intensities of (002) and (020) reflections significantly changed with increasing the composition x, implying the coexistence of the orthorhombic and tetragonal phases. From the solid-state ⁷Li NMR spectra, it suggests that the Li⁺ cation occupies the octahedral site in the composition range of 0 - 0.01, while two signals around -1 and 4 ppm are observed for x = 0.02, suggesting that Li⁺ cations occupy both the A- and B- sites in the lattice at x = 0.02. Such the mobility of Li⁺ cation to occupy both the A- and B- sites is considered to relate with the evaporation of K in the KNN ceramic during sintering. The d₃₃ values of the ceramics extremely increased from 98 to 198 pC/N by BLN addition in the composition range of 0 – 0.01. Further addition of BLN led to the decrease in the d₃₃ value. The enhancement of the d₃₃ by BLN addition may relate with the coexistence of orthorhombic and tetragonal phase in MPB region.