Investigation of new lead free (1−x)KNNS–xBKZH piezo-ceramics with R–O–T phase boundary

In this work, lead free piezo-ceramics of (1−x)K_0.4Na_0.6Nb_0.96Sb_0.04O₃–xBi_0.5K_0.5Zr_0.9Hf_0.1O₃ [(1−x)KNNS–xBKZH] have been synthesized by conventional solid-state sintering method. The effect of BKZH content on the phase structure and electrical properties were systematically investigated. The results show that a coexistence of rhombohedral–orthorhombic–tetragonal (R–O–T) phases have been found when x = 0.04, indicating that BKZH doping can induce the formation of R–O–T phase boundary by increasing T _R−O and decreasing T _O−T simultaneously in KNN systems. In addition, an optimal electrical properties (e.g., d ₃₃ = 451 pC/N, k _p = 52%, T _c = 258 °C, ε _r = 2489, tanδ = 3.6%, P _r = 21.7 μC/cm², and E _c = 10.1 kV/cm) were obtained in the ceramic of x = 0.04, which proves that adding BKZH content is an efficientive way to promote the electrical properties of potassium–sodium niobate ceramics. As a result, we can believe that the (1−x)KNNS–xBKZH ceramics will become one of the promising lead-free candidates for piezoelectric applications.