Evolution of phase structure, microstructure and piezoelectric properties in (1 − x)(K_0.4Na_0.6)Nb_0.96Sb_0.04O₃–xCa_0.1(Bi_0.5K_0.5)_0.9ZrO₃ lead-free ceramics

New lead-free piezoelectric (1 − x)(K_0.4Na_0.6)Nb_0.96Sb_0.04O₃–xCa_0.1(Bi_0.5K_0.5)_0.9ZrO₃ ceramics were projected and prepared by using traditional ceramic preparation techniques, and we investigated the effects of Ca_0.1(Bi_0.5K_0.5)_0.9ZrO₃ content on their surface microstructure, phase structure and electrical properties. A phase pure perovskite structure was obtained for the ceramics within the studied composition range of 0 ≤ x ≤ 0.06, according to X-ray diffraction analysis. Additionally, it was found that adding Ca_0.1(Bi_0.5K_0.5)_0.9ZrO₃ into the ceramics caused a gradual evolution in the phase structure, and a rhombohedral-tetragonal phase boundary was identified at the composition x = 0.04. The ceramics showed an enhanced piezoelectric activity with compositions near the phase boundary. Furthermore, the phase diagram of the (1 − x)(K_0.4Na_0.6)Nb_0.96Sb_0.04O₃–xCa_0.1(Bi_0.5K_0.5)_0.9ZrO₃ solid solution was built up by combining the X-ray diffraction analysis with the measurement results of the temperature-dependent dielectric behavior. These results indicate that the structural state of (K,Na)NbO₃-based ceramics can be easily altered by using a suitable amount of Ca_0.1(Bi_0.5K_0.5)_0.9ZrO₃ as additive, which will benefit the improvement of piezoelectric properties for such lead-free materials.