Thermally-driven unequal cation vacancy formation and its effect on the dielectric properties in K_0.5Na_0.5NbO₃ ceramics

The formation of cation vacancies can be useful for electro-chemical devices. In this regard, an understanding of vacancy formation is an important subject for enhancing current electrochemical devices and for developing next generation energy devices. In this work, we chose the well-known lead-free ferroelectric (K_0.5Na_0.5)NbO₃ (KNN) as a model system to understand both the formation of cation vacancies and the relationship between cation vacancies and the physical properties. We studied sintering-duration dependence of the dielectric properties and the cation contents of KNN ceramics at the temperatures near the melting point of KNN. The difference in sintering duration led to a drastic change in the dielectric property, as well as to the creation of cation vacancies. Interestingly, we observed unequal evaporation of cations during the sintering process, which was confirmed by the data obtained from laser-induced breakdown spectroscopy. In addition, we found more drastic changes in the imaginary dielectric constant, which were likely due to a decrease in ionic conducting species, such as K and Na, in KNN.