Piezoelectric and electrocaloric properties of high performance potassium sodium niobate-based lead-free ceramics

Piezoelectric ceramics, as a kind of functional material, can realize the mutual transformation between mechanical energy and electrical energy, and has been widely used in civil and military fields. With the improvement of people's awareness of environment protection and self-health care, the study of lead-free piezoelectric ceramics with excellent performance and environmental friendliness has become an urgent task. Among several kinds of lead-free piezoelectric materials, potassium sodium niobate [(K, Na)NbO₃, KNN]-based ceramics has attracted much attention due to its good comprehensive properties, but there have been carried out few studies focusing on the utilization of phase boundary to regulate the properties of high piezoelectric and electrocaloric effect simultaneously. In this work, lead-free 0.944K_0.48Na_0.52Nb_0.95Sb_0.05O₃-0.04Bi_0.5(Na_0.82K_0.18)_0.5ZrO₃-1.6%(Ag<i>_x</i>Na_1–<i>_x</i>)SbO₃-0.4%Fe₂O₃ ceramics is prepared via the conventional solid-state method, and the effect of AS/NS ratio on phase structure, electrical properties, and electrocaloric effect are studied. The obtained results show that the ceramics has a multiphase coexistence with “rhombohedral-orthorhombic-tetragonal” (R-O-T) in all compositions. With the increase of AS content, the piezoelectric and ferroelectric properties of the ceramics fluctuate (<i>d</i>₃₃ = 518–563 pC/N, <i>k</i>_p = 0.45–0.56; <i>P</i>_max = 21–23 μC/cm², <i>P</i>_r = 14–17 μC/cm²). In addition, the electrocaloric effect (ECE) for each of the samples is studied by the indirect method. Broadening temperature span (～90 K) of electrocaloric effect is obtained in the vicinity of O-T phase transition region, while a low ECE value is observed. A stronger ECE peak (Δ<i>T</i>_max > 0.6 K) can be observed when the measurement temperature reaches near the Curie temperature. Consequently, both large piezoelectric property and high electrocaloric performance can be realized in KNN-based ceramics by new phase boundary construction.