Unveiling the electrical performance of flash-sintered potassium sodium niobate†

In the context of sensor, actuator, and energy harvesting applications, lead-free ferroelectric K_0.5Na_0.5NbO₃ (KNN) ceramics offer several advantages, including a high transition temperature and an elevated piezoelectric coefficient. However, producing single-phase KNN ceramics at a low thermal budget requires alternative sintering processes such as electric-field- and current-assisted flash sintering. Furthermore, the electrical properties of flash-sintered ferroelectrics are rarely disclosed. Here, based on systematic dielectric and ferroelectric, impedance spectroscopy and DC conductivity measurements, we demonstrate that the electrical performance of flash-sintered KNN is quite dependent on its thermal history, in contrast to the conventionally sintered one. Simultaneously, we demonstrate the successful production of high-performance KNN ceramics with high polarization, dielectric permittivity, Curie temperature, and piezoelectric coefficient using flash sintering, coupled with a carefully chosen post-sintering electrode curing step. Supported by impedance spectroscopy results, indicative of enhanced oxygen vacancy content in flash-sintered KNN, we postulate that post-sintering heat treatment and low-thermal-budget flash sintering are equally critical for KNN applications, complementing the benefits of reducing lattice defects and enhancing electroceramic performance. Our results demonstrate a pathway towards alternative sintering of electroceramics and offer opportunities to control performance.