Structural and compositional indicators of ferroelectric properties of KNN ceramics

Abstract

Improvement of the properties of KNN ceramics requires tools allowing one to reveal a relation between the structure and composition, on the one hand, and ferroelectric property, on the other. In this work, lead-free (1-x) (K0.5Na0.5)NbO3-xAgNO3 and (1-x) (K0.5Na0.5)NbO3-xBaZrO3 ceramics with different contents of the ferroelectric phase have been studied using piezoresponse force microscopy (PFM), X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS). A correlation between the PFM image contrast, the SEM phase contrast (BEI) and the elemental composition of the phases (EDS) has been found. Specimens with a low content of the ferroelectric phase contain secondary phase with composition and structure different from those of ABO3 perovskite. XPS has shown the presence of two types of potassium ions with different chemical states, i.e., inside (K1) and outside (K2) the perovskite lattice. The observed correlation between the ferroelectric properties of the ceramics and the K2 concentration allows one to use it as a reliable indicator of ferroelectric properties.