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 {110}C and {100}C planes. A one-dimensional {100}C modulated texture is also observed locally. The electron diffraction study reveals the presence of (001)T tetragonal platelets a few cells thick within the R3c matrix. They develop within the three basal {100}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 {100}C modulated texture corresponds to a modulation of strain induced by the coexistence of two types of octahedra tilting systems: aaa for the rhombohedral matrix and a0a0c+ for the tetragonal platelets. These (001)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.