Relaxor or classical ferroelectric behavior in ceramics with composition Sr2-xA1+xNb5O15-xFx (A = Na, K)

By partial cationic and anionic substitutions in NaNbO3-SrNb2O6 and KNbO3-SrNb2O6 systems, two solid solutions have been obtained: Sr2−xNa1+xNb5O15−xFx and Sr2−xK1+xNb5O15−xFx. 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 aferroelectricrelaxorbehavior. Such relaxorferroelectricceramics with lead-free compositions can be of great interest for environment-friendly applications