A transmission electron microscopy study of the A-site disordered perovskite Na0.5Bi0.5TiO3

A transmission electron microscopy study of Na0.5Bi0.5TiO3 (NBT) crystals shows two types of ferroelectric domains characterized by interface boundaries lying in the {1 1 0}C and {1 0 0}C planes. A one-dimensional {1 0 0}C modulated texture is also observed locally. The electron diffraction study reveals the presence of (0 0 1)T tetragonal platelets a few cells thick within the R3c matrix. They develop within the three basal {1 0 0}C planes of the prototype phase and represent relics of the high-temperature tetragonal phase. The loss of symmetry compared to the average structure of NBT can thus clearly be attributed to the existence of these tetragonal platelets. The {1 0 0}C modulated texture corresponds to a modulation of strain induced by the coexistence of two types of octahedra tilting systems: a−a−a− for the rhombohedral matrix and a0a0c+ for the tetragonal platelets. These (0 0 1)T platelets indirectly intervene in the relaxation process classically encountered at about 230 °C, in marked contrast to the behaviour of Pb(Mg1/3Nb2/3)O3.