Properties of morphotropic phase boundary lead barium niobate (PBN) compositions

Abstract

Investigations of the polarization mechanisms in tungsten bronze ferroelectric, Pb_1−xBa_xNb₂O₆, in particular of the morphotropic phase boundary compositions, have been carried out for both ceramics and bulk crystals by means of electrical, optical, and electron microscopic methods. It is demonstrated by optical conoscopic interference figure that electric field can switch the crystal from one ferroelectric phase to the other for compositions close to the morphotropic phase boundary. A TEM study in the temperature range from—180°C to room temperature revealed the presence of ferroelectric domains and discommensurate structures associated with octahedral rotations in the PBN crystals and ceramics. In the light of above observed experimental data, the polarization mechanisms of the morphotropic phase boundary compositions are discussed.