Ferroelectric domain morphology evolution and octahedral tilting in lead-free (Bi_1/2Na_1/2)TiO₃-(Bi _1/2K_1/2)TiO₃-(Bi_1/2Li _1/2)TiO₃-BaTiO₃ ceramics at different temperatures

Observations by in situ transmission electron microscopy (TEM) reveal the changes in domains morphology in 0.885(Bi_1/2Na_1/2)TiO ₃-0.05(Bi_1/2K_1/2)TiO₃-0.015(Bi _1/2Li_1/2)TiO₃-0.05BaTiO₃ ceramics. Evolution of the macroscopic ferroelectric domains has been observed at 25°-180°C. The ferroelectric domains and their walls reduce progressively with increasing temperature. In the selected-area electron diffraction patterns, the crystallographic evidence of antiferroelectric domain is not found over the temperature range, which provides the evidence that the ferroelectric-antiferroelectric transition does not occur in the ceramic. The temperature-dependent forbidden 3/2 1/2 0 and superstructure 3/2 1/2 1/2 reflections indicate the presence of an in-phase and anti-phase octahedral tilting in the ceramic, respectively. Dark-field TEM images show that the size of the octahedral tilted domains is smaller than 30 nm across and that these domains are uniformly distributed in the grains. The influence of the localized octahedral titling on the stability of ferroelectric domains and the temperature-dependent properties is discussed in this paper.