Relaxor or classical ferroelectric behavior in ceramics with composition Sr 2− xA 1+ xNb 5O 15− xF x (A = Na, K)

Abstract

By partial cationic and anionic substitutions in NaNbO 3–SrNb 2O 6 and KNbO 3–SrNb 2O 6 systems, two solid solutions have been obtained: Sr 2− x Na 1+ x Nb 5O 15− x F x and Sr 2− x K 1+ x Nb 5O 15− x F x . They crystallize in the tetragonal tungsten bronze (TTB) type structure, which is related to that of the perovskite. The replacement of oxygen by fluorine causes a decrease of the Curie temperature. A weak F–O substitution rate increases the compactness, which leads to higher dielectric constant with good piezoelectric and pyroelectric characteristics. A relatively higher F–O substitution rate induces a ferroelectric relaxor behavior. Such relaxor ferroelectric ceramics with lead-free compositions can be of great interest for environment-friendly applications.