Thermal Stability Enhanced by Short-range Ordered Ferroelectricity in K0.5Na0.5NbO3-based Oxide

Abstract

Lead-free piezoelectric ceramics have been widely investigated as a replacement for the lead-based piezoelectric materials due to the toxicity and environmental issues of lead. However, the temperature ranges at which the lead-free piezoelectric ceramics can maintain piezoelectric properties is limited below 200°C, and the loss of piezoelectricity is still large within that temperature range. This lack of thermal stability of lead-free piezoelectric ceramics has hindered their use at high temperature environment. In this study, we report lead-free (K,Na)NbO3 (KNN)-based system with remarkably enhanced thermal stability of piezoelectric properties with little loss up to 300°C by exploiting grain size. We synthesized a set of BiScO3 (BS)-doped KNN-based ceramics with a meticulous BS doping control near the optimal chemical composition [1] predicted based on the phase-field simulations and first principles calculations. Through comprehensive evaluation of microstructure by (scanning) transmission electron microscopy ((S)TEM), we demonstrated the correlation of grain size and thermal stability. In addition, we realized the applicability of the thermally stable actuating devices composed of KNN ceramics, and confirmed that the thermal stability of KNN-based ceramics is well reflected when fabricated as devices. This is the first time to achieve lead-free piezoelectric ceramics with an outstanding thermal stability up to 300°C and suggest an applicability as an actual device with highly stable piezoelectricity. [1] M. K. Lee, S. A. Yang, J. J. Park, & G. J. Lee. (2019). Proposal of a rhombohedral-tetragonal phase composition for maximizing piezoelectricity of (K,Na)NbO3 ceramics. Scientific Reports, 9(1), 4195.