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

TLDR

Lead‑free piezoceramics are pursued for environmental reasons, and polymorphic phase transitions have been used to tailor their properties, though such transitions typically cause large temperature sensitivity. The authors report a material concept that achieves an average piezoelectric coefficient d33 of about 300 pC/N and a high unipolar strain of up to 0.16 % at room temperature. The temperature insensitivity of field‑induced strain is rationalized by electrostrictive coupling to polarization amplitude, while the temperature‑dependent piezoelectric coefficient is examined via localized piezoresponse probed by piezoforce microscopy. Field‑induced strain varies by less than 10 % from room temperature to 175 °C, demonstrating temperature‑insensitive performance that opens a new development window for piezoelectric actuators despite a polymorphic phase transition near room temperature.

Abstract

Abstract 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)NbO 3 (KNN)‐based materials accepting the drawback of large temperature sensitivity. Here a material concept is reported, which yields an average piezoelectric coefficient d 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 °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.