The effect of BaZrO3 content on the structure, microstructure, and electrical properties of (K, Na)NbO3-based lead-free ceramics

Abstract

This study used two-step sintering to prepare lead-free (1–x)[(K_0.48Na_0.48Li_0.04)(Nb_0.95Sb_0.05)O₃]– xBaZrO₃ [(1–x)KNNST–xBZ] ceramic samples with x = 0.0, 0.015, 0.03, 0.045, and 0.060. The influence of the content of BaZrO₃ (BZ) on the structure, microstructure, and physical properties of the (K_0.48Na_0.48Li_0.04)(Nb_0.95Sb_0.05)O₃ (KNLNS) ceramic was studied in detail. Experimental results showed that the KNLNS crystal structure transformed from the orthorhombic phase to a rhombohedral phase to construct the new phase boundary near room temperature for 0.03 ≤ x ≤0.045, improving the electrical properties of the ceramic at the optimized BZ content. Raman scattering, X-ray diffraction, scanning electron microscopy, and the electrical properties of the samples showed that the optimal BZ content was 0.03 mol, corresponding to the solubility limit of Ba²⁺ and Zr⁴⁺ ions in the KNLNS ceramics. Furthermore, substituting Ba²⁺ and Zr⁴⁺ at the A- and B-site induced lattice distortion in the (1–x)KNLNS– xBZ structure to increase the relaxation behavior and decrease the T_O−T values sharply to 45 °C, which was the optimum poling condition that could develop the possible piezoelectric properties. At the optimized BZ content of 0.03 mol, the 0.97KNNST– 0.03BZ ceramic had the best electrical properties: density = 4.56 g/cm³, dielectric constant (ε_r) = 1130, electromechanical coupling factors k_p = 0.39 and k_t = 0.40, piezoelectric constant (d₃₃) = 225 pC/N, remanent polarization (P_r) = 15.2 µC/cm², and normalized strain (d₃₃^*) = 470 pm/V. The highest Q_m value of 102 was for 0.045 mol BZ.