Temperature-Insensitive (K,Na)NbO3-Based Lead-Free Piezoactuator Ceramics

The development of lead-free piezoceramics has attracted great interest because of growing environmental concerns. A polymorphic phase transition (PPT) has been utilized in the past to tailor piezoelectric properties in lead-free (K,Na)NbO3 (KNN)-based materials accepting the drawback of large temperature sensitivity. Here a material concept is reported, which yields an average piezoelectric coefficientd(33) of about 300 pC/N and a high level of unipolar strain up to 0.16% at room temperature. Most intriguingly, field-induced strain varies less than 10% from room temperature to 175 degrees C. The temperature insensitivity of field-induced strain is rationalized using an electrostrictive coupling to polarization amplitude while the temperature-dependent piezoelectric coefficient is discussed using localized piezoresponse probed by piezoforce microscopy. This discovery opens a new development window for temperature-insensitive piezoelectric actuators despite the presence of a polymorphic phase transition around room temperature.