Microscopic Insight into Electric Fatigue Resistance and Thermally Stable Piezoelectric Properties of (K,Na)NbO₃-Based Ceramics

Pb-Based piezoelectric materials such as Pb(Zr,Ti)O3 have been the mainstay for electromechanical devices; however, they encounter the challenge of sustainable environmental development, which requires Pb-free piezoelectric counterparts. The foremost obstacles in developing Pb-free piezoceramics are their low piezoresponse and inferior temperature stability. In this work, we reported Mn-modified ⟨00l⟩c-textured (K,Na)NbO3-based ceramics to achieve thermally stable piezoelectric properties and enhanced fatigue resistance in conjunction with high piezoelectricity of d33 ∼ 560 pC/N. The in situ d33 measurement reveals that the temperature stability of the small signal d33 is mainly dependent on temperature-induced phase transition. However, the local piezoresponse force microscopy measurements imply that the excellent temperature stability of the large signal d33* (field-induced strain) benefits from the stable domain response to applied electric field at elevated temperatures. Moreover, the good fatigue resistance is proposed to be associated with the decreased defect concentration by Mn doping, based on the analyses of dielectric loss, leakage current, and thermally stimulated depolarization current.