Phase transition and piezoelectric properties of (1−x)(K_0.42Na_0.58)(Nb_0.96Sb_0.04)O₃–x(Bi_0.5Na_0.5)_0.90Mg_0.10ZrO₃ lead-free ceramics

(1−x)(K_0.42Na_0.58)(Nb_0.96Sb_0.04)O₃–x(Bi_0.5Na_0.5)_0.90Mg_0.10ZrO₃ [(1−x)KNNS–xBNMZ] lead-free ceramics have been prepared by the normal sintering, and effects of BNMZ content on their phase structure, microstructure, and electrical properties have been systematically investigated. These ceramics with 0.045 ≤ x ≤ 0.05 possess a rhombohedral–tetragonal (R–T) phase boundary, as confirmed by the temperature dependence of dielectric properties and X-ray diffraction patterns. The grain size of the ceramics first increases and then decreases as the BNMZ content increases, and the ceramic with x = 0.06 possesses much smaller grains (<1 μm), resulting in the abnormal electrical and phase transition behavior. In addition, the Mg²⁺ was homogenously distributed in the ceramic matrixes. These ceramics with R–T phase boundary show enhanced dielectric, ferroelectric, and piezoelectric properties as compared with a pure KNN, and optimum electrical properties (e.g., P _r ~ 16.23 μC/cm², E _C ~ 7.58 kV/cm, ε _r ~ 2,663, tan δ ~ 0.034, d ₃₃ ~ 434 pC/N, k _p ~ 0.47, and T _C ~ 244 °C) were found in the ceramic with x = 0.0475. We believe that the (1−x)KNNS–xBNMZ ceramic is a promising candidate for lead-free piezoelectric devices.