Ferroelectric properties of tetragonal lead barium niobate (Pb_1-xBa_xNb₂O₆) crystals near the morphotropic phase boundary

Tungsten bronze ferroelectrics with a morphotropic phase boundary (MPB) have become increasingly important for a variety of applications because of their enhanced and unique properties near the MPB. Lead barium niobate (Pb_1-xBa_xNb₂O₆) crystals, which have a morphotropic phase boundary between the orthorhombic (1 - x > ∼0.63) and tetragonal (1 - x < ∼0.63) phases, were grown in sealed Pt crucibles by the vertical Bridgman method for tetragonal compositions near the MPB, and their ferroelectric properties were investigated. The ferroelectric domain structures in as-grown crystals were revealed either by etching in hydrofluoric acid or by polishing with colloidal silica, the latter providing clearer features. Domain size on the surface perpendicular to the polar axis was 10-50 μm. Crystals could be poled by slowly cooling from above the Curie temperatures (300-400°C) under a dc field of 5 V/mm. The spontaneous polarization P_s of tetragonal Pb_1-xBa_xNb₂O₆ was found to be in the range of 0.40-0.70 μmC/mm² at room temperature depending on composition and increased as the composition approached morphotropic phase boundary (1 - x = ∼0.63), as expected.