Ferroelectric properties of tetragonal lead barium niobate (Pb1−xBaxNb2O6) crystals near the morphotropic phase boundary

Abstract

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 (Pb1−xBaxNb2O6) 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 Ps of tetragonal Pb1−xBaxNb2O6 was found to be in the range of 0.40–0.70 μC/mm2 at room temperature depending on composition and increased as the composition approached morphotropic phase boundary (1 − x = ∼0.63), as expected.