Crystal Structures and Ferroelectri Properties of SrBi₂Ta₂O₉, and its Degradation under Reducing Conditions

Abstract

Crystal structures and ferroelectric properties of SrBi₂Ta₂O₉, which is used for FeRAM, are reported. Structure analysis using neutron diffraction data reveals significant distortion of the structure. The pronounced structural distortion of the perovskite-type unit leads to larger ferroelectric polarization and higher Curie temperature. Crystal structures and ferroelectric properties of an A-site substitution system, (Ca, Sr, Ba)Bi₂Ta₂O₉, and a B-site substitution system, SrBi₂(Ta, Nb)₂O₉, are also reported. Degradation of SrBi₂Ta₂O₉ under reducing conditions is investigated and the degradation mechanism is discussed from a structural point of view.