Principles and Applications of Ferroelectrics and Related Materials

(Sr0.53Ba0.47)2.5−0.5xNaxNb5O15 ceramics (SBNN, 0.0 ≤ x ≤ 2.5) were prepared by the conventional solid-state reaction method. The Na+ concentration varied from 0.0 to 2.5 so that the tetragonal tungsten bronze (TTB) crystal structure was designed to transform from ‘unfilled’ to ‘filled’ and then to ‘stuffed’ type. Apart from the change in the structural type, the effects of Na+ concentration on the phase structure as well as microstructure, ferroelectric and dielectric properties were also investigated. X-ray diffraction analysis revealed that the crystallized SBNN ceramics with x ≤ 1.0 had the tetragonal tungsten bronze structure with space group of P4bm. With further increasing x above 1.0, the broad asymmetrical diffraction peaks near 32° associated with EDX analyses indicated the existence of some amount of secondary NaNbO3-based phase due to the introduction of excessive Na+. It was also found that Na+ concentration had a significant influence on the electrical properties of SBNN ceramics. Introducing Na+ in A-sites to decrease the structural vacancies and increase the distortion degree of NbO6 polar unit was beneficial for the electric properties, while excessive Na+ content would deteriorate the electric properties owing to the presence of secondary NaNbO3-based phase.