In-situ observation of the domain configurations during the phase transitions in barium titanate

Using a polarizing optical microscope in conjunction with a charged-coupled device camera system, the domain microstructural evolution with respect to temperature in all three phases of BaTiO₃ was studied. Along a (001) oriented section the domains in the tetragonal phase form 90° domain patterns in an ‘a—a’ configuration. The transition on heating and cooling between the cubic and tetragonal phases occurred near the same temperature, 125°C. On cooling, the domain structures in the orthorhombic phase appeared as a long continuous lamellar structure, while on heating the domains formed a ‘patchwork’ structure. This transition temperature showed a large thermal hysteresis. The final transition temperature from orthorhombic to rhombohedral was difficult to determine using this technique. The transition on cooling occurred at −134°C based on a colour change and the disappearance of all the domains. During heating, the domains reappeared at −110°C and remained in a patchwork structure throughout the orthorhombic phase.