Ferroelectrics in the k2O-SrO-Nb2O5 system

Abstract

Research into the tungesten bronze phase field of the K2O-SrO-Nb2O5 system (KSN) has shown that ferroelectricity occurs over a wide range of compositions close to the KNbO3-SrNb2O6 binary line. The approximate location of the congruently melting composition was found by chemical and X-ray analyses of crystals produced from vertical float zoning and Czochralski pulling experiments and was centred on k2Sr9Nb20O60. This composition gave crystals of much improved optical quality-free from striae but containing vertical structure.K2Sr9Nb20O60 crystals have distinctive dielectric properties, the dielectric constant of poled crystals being half that of the as-grown ones. The true lattice spacing in the 'c' direction is double that of the basic tetragonal unit cell and may be explained in terms of tilted NbO6 octahedra.The low half-wave voltage and dielectric properties of K2Sr9Nb20O60 make it potentially useful for electro-optic and pyroelectric applications. However, the reproducibility of striae free crystals pulled from the melt has not been proven.