The structural origin of the antiferroelectric properties and relaxor behavior of Na0.5Bi0.5TiO3

This work presents a study of Na0.5Bi0.5TiO3 (NBT) by transmission electron microscopy in the 20–370 °C temperature range. A new orthorhombic intermediate phase between the rhombohedral and the tetragonal phases is proposed to account for the occurrence of 12(oee) superstructure spots. The phase transition from the rhombohedral to the orthorhombic phase occurs via a modulated phase formed by rhombohedral blocks and orthorhombic sheets. It is shown that these latter represent rhombohedral (0 1 0) twin planes. The modulated phase is proposed to explain the antiferroelectric and relaxor behaviors of NBT.